As for the mega pixel monster, I think it is going get a smaller number in front of the D, it might be 2, 3 or 4. Since 3D might be misleading <snip> my bets are on 4D. The smaller the number, the pricier. And if it really is the 4k cinema camera, 4D makes sense.
It's extremely unlikely that you'll see a camera called a 4D. The number 4 is strongly associated with death in many Asian cultures, including that of Japan. When I worked in Hong Kong, my hotel didn't have a 4th floor; the button panel in the elevator went 1-2-3-5-6[...] It's a lot like the number 13 in the US.
I suspect "3D" or maybe "1DSX" are more likely candidates. But does it really matter what Canon calls the camera? The photos I take with my 7D wouldn't look any worse (or better) if Canon instead named it the Barbie Super-Fun Photo Cam.
So, what about the 1DMkIV? I maybe wrong, but I do not consider it as very likely not to produce a 4D. Let's get serious: Does any worker at Canon refuse to work on a 4th every month? Nothing intended, just don't take anything of that without a good grain of salt. I once experienced something here in switzerland. I bought some trousers. But the had to tailor it back to my leg length. So the seller said: I have just one question, Sir. Do you mind if we prepare them for the 13th? I said, no. And asked her back: I guess you don't deny your thirteenth salary at the end of year either (swiss workers receive a thirteenth salaray by xmas). So she was puzzled for a moment and stuttered: Of course not! You are absolutely right!