I got a few ideas of my own:
1. The reforging system for weapons in Terraria is good, though it encourages a lot of people to spend a lot of coins to get the best modifier out there on their weapons, which is why I think some of the modifiers need to be balanced. The best modifiers, the trashy modifiers, and modifiers like Light or Ruthless will remain the same, while the in-between modifiers can be buffed to the point where they are more viable than the best modifiers in specific scenarios, but overall are still worse.
2. On the topic of reforging, I think accessory modifiers have a lot of potential. Adding other types of modifiers could allow for Terraria players to have more control over their loadouts. A few of my ideas would be modifiers that increase the projectile speed of ranged weapons, or one modifier that increases life regen slightly, modifiers that decrease the use time of all weapons (by either 1 or 2 percent, as not to make the melee speed modifiers obsolete), or modifiers that increase armor penetration.
3. I saw someone post the idea of a "wrap-around world" earlier in the thread, and I'd agree, that would be really cool. But allow me to expand on this with an idea I came up with fairly recently. What if you were able to, rather than having a looping world, tie two worlds together, e.g. walking to one edge of a world loads in another world and puts you at the edge of that one?
Also, to be honest, a Gauntlet in Terraria would be pretty overpowered. After playing with my own overpowered Terraria mods for a while, I realized that Terraria is fun because it's hard, and overpowered items make the challenge of bosses obsolete. Having a gauntlet in Terraria might be fun for a while, but pretty soon people would be asking for a boss that could match the power of the Gauntlet, and then the people would ask for a Super Infinity Gauntlet, and then a Super Boss, ect... which eventually would turn Terraria into a power struggle rather than a true challenge.