1 - Piping System
That could work very well. Then you could run pipes to certain areas, like a central drop point where numerous tunnels connected.
I'm assuming this is like some of the piping in Minecraft, where you will be able to place it beside a chest and the items in the pipe will automatically go into the chest?
Different colored pipes would be good, to color code them and give you a way of organizing your pipes. But maybe also special connectors at the ends. To be combined with a chest.
Say a Red Connector will pull items from the chest beside it and send them down the pipe.
A Blue Connector will deposit items into the chest beside it.
You could then place a Connector on either side of a chest, to extend the range of a pipe, while allowing you a manual drop point.
If that is confusing, here is a bit more of a detail. You have a large station built about halfway between the Hell Layer and the Surface. You have pipes running straight up to the surface. Blue at the end to offload pipe items into the chest at the Surface, Red at the end to withdraw items from the chest at the Station.
You then connect a new set of pipes running to Hell, with Blue at the Station chest, and Red down in Hell. So basically you put items into the Hell chest, it is piped up to the halfway station, which grabs them and pumps them on up the path to the Surface.
This way, if you are mining around the Station area, you can go drop items in the chest to go to the Surface. If you are in Hell, you can do the same. But when you are in Hell, it negates the need to visit the Station to restart the pump mechanism to finish sending items to the Surface. You could go from Hell to the Surface, and back, without ever having to stop at the Station to make the item transfer. Similarly, you could work around the Station level and the Surface, without having to change your pump system any.
2 - Turrets
I see a variety of these, with different options for usage. And of course, different requirements to make and use. Primarily so we have more to play with than just one type of turret, and also to make them available more fluidly throughout the game.
Low Tier Options:
The Porcupine: Materials used include Wood, a Chain or two, maybe a Dart Trap. This one uses Wood as ammunition. You could hover over it to see how much ammo it currently holds, out of a possible 999. So a full stack of Wood. To load it, you stand beside it and use Wood on it, the way you use Silt in the Extractinator. Basically it launches sharpened wood stakes. The limitation is you have to harvest wood and reload it from time to time. And the damage would be low, since this is an early game turret. Meant for weaker enemies mostly.
Sand Blaster: Materials used include Sandstone, Wood, Chains, and a Dart Trap. This one uses Sand as ammunition. Same basic premise as the Porcupine, however the sand does more of an Area of Effect damage, capable of hitting several enemies in a small area. So if you had 5 enemies gathered right in front of a door, as they sometimes do, this would blast them all. The fine sand would blast out in a pressurized spray, and scour flesh from them. (-insert diabolical laughter-)
Higher end turrets on the Low Tier could use Cacti as ammunition, or more specifically the thorns of a cactus, to cause more damage than the wooden stakes.
Mid Tier Options:
Fire Quill: Basically an updated Porcupine, that uses Fire Arrows as ammunition. Capacity is a full stack of them.
Burning Sands: Updated Sand Blaster, this one uses Sand as well, and requires torches or lava buckets for crafting them. Something based around a LOT of heat. The sand is heated and the spray is similar to a Sand Blaster, but with heated sand, the damage output is higher. (And hot sand flung at you is definitely a PAIN.)
Other options for Mid-Tier items would be a Flamethrower, that could cause a burning debuff on enemies. A turret that used glass for ammunition, breaking it up to a fine powder and launching it for damage and AoE similar to the Sand Blaster, but with some kind of debuff that blinded monsters.
Other options for turrets that aren't so...specialized...would be ones that could use Arrows and Bullets. This way you have ammunition that increases in damage as the game progresses. Of course, there is a difference. With using the existing ammo, the turret would draw damage values from the ammo placed inside. With the specialized versions, damage would be fixed based on the turret, I think.
Other optional ammo types, would be blocks, such as dirt, mud, clay, stone. Or maybe I'm just going too much of the mad scientist here.
Now for some other ideas....
Summons:
I love summons, so why not more 'device' types, as opposed to the magical/natural creatures we have now. In general, all the summons I've seen either fall into two types. The magical creatures or natural ones. So basically a Wizard summon or a Druid summon, in Dungeons and Dragons terms. That leaves us with Constructs, or golems.
To adhere more strictly to the "device" category, these are all more mechanical in nature.
1. Robot NPCs: These are all basically mechanical versions of the vanilla NPCs, with differing damage styles based on what they are.
Guide - Melee attacking
Dryad - attacking in the form of a nature spell
Demolitionist - attacking with grenades that explode on contact with the enemy. Sort of like an RPG (rocket-propelled grenade).
Arms Dealer - attacks with a gun or pistol
2. UFO - flies around in the air, zapping enemies with a beam weapon
3. Metallic Golems
About twice the size of the player character, based around metals. The better the metal, the more damage they can inflict. These would become obsolete as newer ones were made available. Unless you could enforce a limitation on the number that could be summoned, regardless of Armor Bonuses. I'm not sure what the upper limit is with armor bonus. Something makes me think either 3 or 5. So if you went with 5...
Copper -- up to 5 at a time
Iron -- up to 4 at a time
Silver -- up to 3 at a time
Gold -- up to 2 at a time
Then when you get to Hardmode, it'd reset back to 5 for the lowest quality hardmode ore, and go back down to a lower amount for the higher version. Or if this wasn't possible, then maybe each of the Golems could inflict a different type of status effect, in addition to damage. So they aren't entirely useless once you get a better version, depending on your playing style.
Of course, with added status effects for golems, it opens the way for accessories that influence these with your summon. So if a golem inflicted a status that caused the enemy to burn and take damage, the accessory you have for that one could extend the duration of the debuff.
Okay...I guess I should go back to other devices.
Drilling Device - Either limited use, or requires some form of fuel to run. So you either craft a bunch of them to use, or you have to keep getting fuel to put in. Acts like an NPC, since I think that is the only way a non-creature can actually move?. So you drop it out of your inventory, give it the fuel, and it immediately starts to dig. The catch is, it only digs a hole straight down, two blocks wide. But will go as long as it has fuel. Sort of like an auto-Hellevator item. It could have an inventory like a chest, where all blocks it encounters would fill into this inventory for you to harvest.
You could then provide limitations or enhancements. The standard version could act like a lower quality Pickaxe. Better versions could allow for the harvest of better quality ores. So you can't get a freebie with mining stuff you normally wouldn't be able to at that level.
If you can get a Mining Elevator to work, then it seems logical to produce a normal elevator as well.
How about a sorting chest? With your pipe system, if you designed a special chest that worked sort of like an old television splitter. One input (from a pipe) that came in from the bottom. You could place the chest on top of the pipe, if the pipe were a block. Or a special block the pipe fastens to.
The outputs could be on the sides. You could have two special slots in the chest, to place an item into, and it goes by the type to direct the flow.
So a Block would send all blocks through the output, a Brick would instead send all bricks. Put in a weapon and all weapons go through, a Potion would send all potions out. Or maybe this would be too much hassle. But I think a lot of people who sort their stuff via chests, could appreciate dumping it all into one and letting automation sort for them. Rather than stopping at each chest and doing the Quick Stack to dump similar items in.
It would be slightly limited, but sorting options could include:
Weapons, Armors, Accessories, Blocks, Bricks, Walls, Potions, Vanity, Placeables, Chests
Atmospheric Water Generator - The A.M.G. would be an item that you can place, preferably on a small plot of land floating in the air above a chasm in the ground. It pulls water from the air and outputs it (hence the need for it to be over the chasm).
I dunno about most, but I like to play with water. But using buckets or pumps takes a while. Especially if I'm trying to construct a secret base of mass dest....um...water gardening. >.>
So this could pull water out of the air, although you'd need some sort of shutoff. So a Water Sensor would work. It could either send a signal until water was above it (so when the signal stops the A.M.G. stops), or it sends a signal only while water is above it. But then it'd be useless with an A.M.G.
Now that I mention sensors, it sparked a few more ideas.
Clock Sensor - Sends out a signal at a specific Terrarian Hour. This is like the day and night sensors, but it only works once per day. Why? Well...why not?
But it could make for more fun device chicanery. It seems like it'd work best if you made a single one, and you interact with it to set the time. A basic version could work only on a certain hour (ie, 3am, 4am, 5pm, 12am, etc). An upgraded version could then had half-hour capabilities. So it could be 3am, 4:30pm, 12:30am, etc. Sort of like the watches you get, which could be part of it's construction. To go down to a 15 minute interval would be the final step. It largely depends on HOW you wish to use it.
Now we get to timers.
We have the timers for various seconds to send a signal. However, I haven't yet seen a timer that runs for a limited time, then shuts off.
This could open up a possibility for people to build death traps and things for friends to run through. Basically the number on it is how long it sends out a signal once you turn it on, then it shuts off. You have to manually turn it back on. Or, a wire signal could turn it back on.
The timed intervals could be in seconds:
90, 60, 45, 30, 15, 10
Either you make a single timer where you can cycle through the intervals to select the one you want, or you make them like the existing timers, but instead of a red number, make it blue so it is visibly different.
Options for this? Well...uhm. You use a Clock Sensor to turn on your 90 second timers at say...6am. The timer continually sends out it's pulse for 90 seconds. xD I kind of...lost where I was going for the purpose of these two. But I'm sure it was something intricate...and possibly evil.
I know you could combine this with the Portcullis idea. At least for the timer to trip it open, but only for a certain amount of time. Like some of the doors in the Prince of Persia series. Also good for an automatic door to a trap room, that would allow a bunch of zombies at the door to come in, with it slamming shut a few seconds later.
But that could technically be done by you clicking a switch. But then how could you recline back and laugh twistedly as they are mown down by your turrets?
Moving forward with the Generators talk...
For underground, lava in the Thermal Generator was already mentioned. A water mill would be another possible one. But would require water flowing past it like a stream, to generate a wire pulse. That wire pulse could in turn power some things, but also power a pump system to return the water to the top, so it was a never-ending stream.
Wind could be a power source, based on block height. The higher up it is, the more it could generate. Similar to one in a Minecraft Mod.
I'd like to see lights that only worked while the wire signal was being sent. Not the way it is now, where the wire signal simply turns it on or off. But more like real lights. As long as there is a signal, they are working. But if the signal stops, it all goes dark. I definitely like realism in stuff.
Okay, that's all I have for now.