Just my Five cents here :

Multiplayer is OK but if the game becomes a clone of Diablo : No Thank you... 1 million people all trying to level at the speed of light replaying the same level over and over again : BORING...
Multiplayer also demands a serious investment in server-space, development, support, etc... I prefer that the Lar-guys and girls put their energy in DD2 instead of the multiplayer-version if R˛.

However, I hope that DD2 will indeed have a multiplayer option but with the my first remark in place : no copy of Diablo please.