SimWorld

I envision a series of games from Maxis that all work together and are played online.

SimUN,SimNation
These games are focused around politics and there's not too much detail work.
SimCity
Just like the current SimCity but plugged in to this universe.
SimNeighborhood
This is the successor to SimTown. It allowssyou to control a neighborhood within a SimCity. You would control the building that go up (and down) and be an advocate for your sims.
The Sims
Just like the current version but plugged in to this universe.

I believe that there is a distinct possiblity that this will come to be. Maxis has already started down this road with The Sims Online and SimCityScape.