Hopefully, the new MMO won't be the next game in the Diablo franchise. Raiding the Prime Evils would ruin the feel of the game(the lone hero against great evil thing).
EDIT:
It looks like Diablo 3
is going to be an MMO afterall:
Blizzard Entertainment - Employment Opportunities
The first line form the job post kind of gives it away:
"Blizzard Entertainment, the developer of Diablo and Diablo II, is looking for a lead 3D environment artist skilled at creating models and texture maps for both architectural and natural environments."