D3's original incarnation was going to be an MMO. Blizzard submarined that idea and redeveloped the whole game to be what we eventually recieved.
Also, don't underestimate the PR and good will damage done to the Diablo franchise by D3. It failed to step into the shoes left for it by it's predecessors and while the patches have continuously improved it, it is safe to say that people might be very leary of anything released that's associated with Diablo for the next while.