Speaking as a professional game developer, I'd be against this idea. Adding a unified currency into any game creates a very restrictive environment and adding it to a game which has a system where those purchases create advantages for the player makes this worse. In the gaming community this is known as "Pay To Win" or P2W and is currently frowned upon. Diablo 3 gets a lot of flak for this.
I suppose individual game developers could choose to use the currency or not. I don't see how it's a bad idea just because you wouldn't use it. Also what about for ARG's (alternate reality gaming)?