Dokh... I 100% agree with you. I see the rumor mill has already started on this, and the same old stuff is being said about "Blizzard will NOT release during summer... Blizz has to wait so long after announcement.... Blizz will wait until Christmas of 2014 to release... etc etc"
Didn't the release cycle of MoP prove ANYTHING to people that Blizzard does NOT have to follow a script on all things.
But I do think that your time estimate is realistic considering two things... MoP Patch release cycle and the fact that there are multiple teams working on different aspects of WoW, not ALL of them are working on the patches. Some are working on next expansion, some are working on artwork and models.... etc. So the next expansion is already in development and has been for some time.