That's why I was considering something along the same lines as BM—or, perhaps more accurately, like WI. Something where each player can log on, do what they have to do, and when everyone's gotten their stuff in, things can move along.
The basic idea would be that the DM has control over everything but the characters' own persons—and that includes having control over the characters' positions, so they can't go gadding about without him being able to react—and players essentially "propose" actions, which the DM can then confirm, modify, or deny. Everyone, of course, can talk all the time. Talking is a free action 
I think you just re-invented play-by-(e)mail roleplaying. (and SpellMaster) :-)
The problem with this is that you lose one of the most important tools of storytelling: Pacing. You have to make it up somehow. In SM I had something, for a D&D thing you'd have to come up with something.
