This is all guessing. I do think I'm going to be close though. This is what I feel the order and rough time releases will be for Blizzard over the next 3 years.
February - Starcraft 2 Beta begins
May - Starcraft 2 Launches
October - WoW Catclysm Launches
November - StarCraft 2 Expansion
April - Starcraft 2 Expansion
June - WoW Major content patch
October - Diablo 3
March - Unannounced WoW expansion
November - New MMO
I think Starcraft 2 is pretty easy to map out. It is due the first quater of 2010 and based on everything seen it is nearly done. The public beta is really the only thing remaining. WoW wont last another year without Catclysm launching so that has to come by the end of 2010. The SC2 expansion are planned one every 6 months so that is easy aswell. Diablo 3 appears to be about 75% done and considering the void in the Holiday season of 2011 that is a perfect time to launch that.
The catch is another WoW expansion versus Blizzards new MMO. Before I really drew out a calendar I would have bet that the new MMO would release before another expansion after Catclysm... but I just don't see that happening.
Blizzard will try to avoid launching 2 games at once and with 4 titles that is going to be hard to balance. WoW wont last until the end of 2012 without another expansion. However I think the MMO market is more than ready for a new MMO.
The more I think about it the more I want to say Blizzard's new MMO will be out prior to Nov 2012 but considering Blizzard's average development time and the fact that we know NOTHING about it yet makes me think 2 1/2 years or more.