I would say yes, but it would have to confirm if you wanted to lie how the current painkiller / soul flask works.
Depends what they would give in return. If you swipe and never get it back then there are only 3 towers i never use so that wouldn't even form one. Items there are quite a few and some on and off like the rings. It really depends on whether if we don't use we get a chance of getting them back.
I wanted this so badly when I was starting, but I would ultimately say no. Either it's worthless or overpowered. Worthless if they simply make a Rare items from being transmuted. Overpowered if they make another Unique.
hmm. actually, let's say you trade in four unique items and it gives you a random unique item. you might get something less useful like..a second reaver. but maybe you might get lucky and get a second blade of darkness. or I dunno. a second selenreiser. I kinda like that it allows for really lucky people to get an insane boost that would only be doable late game. I'm not sure about how it'd work if items turn into potions tho, could be a gamble, trade in four items for a shot at a second tear of the gods, but it might just be a painkiller.