Guessing
5.2= 03/13
5.3= 05/13
5.4= 09/13
blizzcon= 11/13
beta = 12/13
5.5= 12/13
pre xpac patch= 3/14
6.0 = 4/14
I think MoP will be the shortest exp till now. Year and a half at most.
I'm sure we can all agree that Blizzcon will announce the next expansion; beta will start shortly thereafter and will last 4-6 months. 5.4 will be the last major content patch and will come out right after summer ends and everybody is back from summer vacations and can spend some time playing 5.4. And as always there will be a major patch a month or so before the next xpac which will likely likely include character graphic overhaul; an again modified talent system and pre-expansion storylines. I doubt there would be anything after 5.4 until the pre-expac patch.