There has been more than I can count threads made about this subject, and it never ends well. Most of the people here don't want a Sims to be Multiplayer. Though, some do, but if you want a game that's multiplayer, play Second Life, IMVU, WoW, or anything else like that. Sims in a Single player experience. Even if it's an Expansion, I don't like the idea, and that's just my personal oppinion.
They had a Sims Online back in the beginning, and it ended very badly. So I highly, highly doubt they'll make something that failed another time.