Alchemy
I'd really like to see an alchemy inclusion in the game so that we can use unwanted materials and gems, as well as level up some of our existing items we have no use for.
I would propose that within the new building, we be allowed to use alchemy as a means to level up our diamond knives for example. I currently have more than 500 simple diamond knives, and I would like to be able to level them up for more rare knives, just like we do now for our gems and materials.
What's more, I would like to be able to take gems that I don't want, and use alchemy to change them into gems of other types. For example, I could trade 4 legendary gems of types that I don't want, for one legendary type that I do want. Or whatever number would be deemed such that it won't greatly imbalance the game.
I currently don't even bother leveling up gem types I don't need, but I would level them up even with the higher cost of silver for them, for a chance at a gem I do need, so I really do not think it would really imbalance the game greatly.