I think it'll be very problamatic.
We already had the auction house in diablo 3 and that did not go very well (even though I personally liked it). I'll make farming & hoarding far too easy and people would rather be in this auction house than actually playing the game. I mean, why spendind hours or even days in the game over something you can get in minutes in this auction house?
Not to mention it could devestate the balance in the game. Players could jump from rock bottom to complete dominance in no time.
I'm not completely against it, but think it should be very restricted. Maybe it'll be best just to expand what you could ask for donation inside the guild