Wow, so many responses in such a short amount of time! What a great day for the rumor mill!
Maybe a 4DX or 2DX?
I have to say - this is looking less like a 5DII replacement and more like a 3D/4D/6D/etc. - something in the $4K price range, not a $2.5-3K 5DIII.
It is doubtful that there would ever be a "4D" from Canon, because in Japanese, the word "four" sounds like the word "death." It is considered unlucky.
That being said, the next 5D is "overdue," so I doubt it would be anything other than a 5D III or 5D x. I also think that something "above" the 5D line, such as the mythical 3D, would not have the dial on top.
Has a joystick on the battery grip...
The addition of the joystick on the vertical grip means that the batteries will no longer load via the back. This annoys me on the BG-E6, because it makes the finger hold on the grip thicker and squared off, which is difficult to hold. Hopefully, this means the batteries will go in the side, similar to the 1D line, perhaps with a tray that holds 2 of the LP-E6 (or newer) batteries. This would allow the vertical finger grip to be rounded off, just like the horizontal grip!