I think it wants to be difficult to get early so the potion fits, but maybe it doesn't have to be quite so expensive? To be honest it's probably completely broken or completely useless depending on the board.
I really like the idea. Maybe exchanging them instead of remodeling them would make it less aggressive, thinking about the three pile ending
Yeah that's a good point! I was hoping that you'd get it late enough in the game that it isn't a problem but maybe the piles would just empty before it bites you in the bum too much. I'll make it return to the supply so you still get the on-gain effects. I'll also make it cost $4P because i think $6P might be a little conservative.
So here's the update:
I'd also like to point that the anti-synergy with potion is really strong: If this is the only thing with potion in the kingdom, potion becomes a dead card after you buy this and, on the other hand, if there are other cards with potion in their cost, you probably don't want this.
Also, as you said, this project is board dependent, so I think that it should be easier to get, then, if it's broken, at least you don't have bad shuffle issues. Maybe making this a debt cost card?