I really wish they could move a couple of blocks every few seconds (talkin about the guards)
Animated guards/deco NPCs definitelly are a possibility. So, for example, a blacksmith who's repeatedly hitting and anvill with his hammer or something. I didn't tried making such yet, but it's likely the same sort of stuff like any other animated furniture, like a sawmill for example.
But making them to walk is much more complicated. Furnitures can't walk (as far as I know), so, the only ways to make them able to walk are
- making them into actual town NPCs (rejected, because they're just deco, so it would be bad if they clof the housing menu, when they sell nothing.
- furniture-bound deco NPCs (this might be possible, I'm not sure. but it sounds like a lot of work if we want many types of guards)
...actually... I think, it might be possible though to make guards in a way that they're still furnitures, but, if their animation is, that they walk, that might be possible, but it would, by standard, mean, that they would be very large furnitures, and nothing else could be placed in their walking path (as the whole is the furniture)
this could be modified however maybe, but I don't know how those are coded. There are placeable things that only take up one block, but the thing actually overhangs the block it's placed on (strange plants, and most dye plants work like this) - this could mean, that it would be possible to make guards that are still furnitures, take up only a small space, and still able to walk, without actually being an NPC.
However this sounds complicated, and my main problem with it is the ridicolous spritesheet of town NPCs. each town NPC have a crazy amount of sprites in their spritesheet, so, making such for all these guards would be a real lot of work, and I don't feel inspired to do that.
The fossil pickaxe sounds nice but it feels too niche if it's just for them, how about it worked like the Silk Touch enchantment from Minecraft ? It would allow you to mine blocks that would usually break into something else like fossils, gems and bone blocks without them breaking into their components. It's still a niche item but it would give it a lot more uses.
Marketplace vendors as decoration are a great idea but making them a full on shop is more complicated, it's fine with some items normal items like silk but I'm not a fan of taking away stuff from a full NPC just to give some things to a crafting station
Silk touch sounds interesting, but the problem is, that many of the "special" blocks have no item (placeable block) counterpart that could drop. for example, living leaf block.
as for marketplace vendors, I mean, not to take away stuff from the actual NPCs (since they're more convinient anyway, having normal shops) but a way that you could make something like a marketplace. It actually could be just deco NPCs, but, if they are market vendors, it might be better if they also have items they "sell".
Though, it could be, they are crafted with the items they sell, so, let's say, you have an apple vendor - let's say, something like an old grandma' - crafting her stall (which includes her, since she's part of the furniture) requires, let's say 5 apples, in addition to other stuff. So, you can only make the market stall, if you already have some of those items. But after that, you could buy (craft) said item at the stall (for coins)
Of course, it's not very useful (though might could look good) with apples, and getting 5 apples normally would be nonsensically difficult too (this is where the waiter (or cheat sheets XD) could help.
it sounds easier to make stuff like a silk-vendor this way, but you have no real need of that - but might be fine for deco and atmosphere.
but with some other items, it might would be handy? Though, what sort of items?