In the past, the 5D series has been upgraded every three or more years. Canon invests a huge amount of money in the upgrades, and wants to have some real improvements before releasing a new model.I agree Mt. Spokane. And there is something really tingilly about the sound 5Dx... Mmmm...
The Rebel line is upgraded yearly with minor changes, because the general buyer wants the latest model, and often does not really know what the difference in models may be.
That said, there may very well be a new higher mp body with something like a 5DX designation, but there are no reliable rumors, and it won't happen this year.
There are rumours that when the 7D2 gets announced in the fall (Christmas in stores?) it will have a new and updated sensor technology. If that is true, you can expect updates of the FF bodies as well, but you would be looking at announcements in early 2014 and in stores the summer of 2014 AT THE EARLIEST!
Realistically you should not expect any FF updates until late 2014 or later. That's a long time to wait for a best case scenario for a possibly rumored camera. The only reason I would wait is if I already had a camera that met my needs, otherwise, how can you go wrong with a 5D3?