Additionally, not all throughput calculations people do factor in the 14fps frame rate of the 1D X (which it can do with mirror lockup.)At 14 FPS, its not just a lack of mirror movement and AF, but RAW is off the menu too - read page 113 of the 1D X manual if you want to check up on it.
It all depends on whether Canon want to make it fast or really fast. In reality, the small mirror could move faster than the 12 FPS full sized mirror in the 1D X does, but something tells me they won't do that for marketing purposes. 12 FPS and a very healthy sized buffer wouldn't be out of the question if the MP is kept down.
Admittedly, your calculations resized to 12 FPS for the 1D X in RAW mode make a 24MP camera with the same processing power capable of 9 FPS, which is a slight improvement over the current 7D.
The pixels streaming in from the sensor are "raw"...it doesn't become a JPEG until AFTER the DIGIC chip has done its work and the image is rendered, compressed, and written to the CF card. The input rate from sensor to DIGIC would have to be 473mb/s regardless of what format you end up writing to. JPEG would only matter for the data writeout rate to the CF card. Writing to CF card is limited to at most 150mb/s, on top of which I believe the 1D X has only a 768mb frame buffer...which wouldn't actually be able to accommodate 14fps continuous RAW for a sustained 3.2 seconds (which is what you get at 12fps.)
I get what you're saying about what comes off the sensor being raw. The digic chip does all the conversion to jpeg after all. But it can't be the CF card which restricts the use of raw, as the data gets stored in the buffer and then it gets dumped onto the CF card in whatever amount of time it takes. After all, a 1D X doesn't slow down with slow cards if the burst can be contained fully within the buffer. Also, the buffer size doesn't impose any limits on speed of the burst, just its depth.
I don't know where the bottleneck with the 1D X is, but it seems like 12 fps is pretty much the upper limit for that FF mirror to flap around as at 14 fps its stays put, disabling AF and the viewfinder. And 12 fps clearly is also the limits of some part of the processing/storage for 18MP raw, as 14 fps is jpeg only. I believe that's why the 1D X has a lower number of MP that other recent FF cameras - the 1D X's electronics couldn't handle more MP while doing the the mirror box justice. No doubt the replacement for the 1D X with its faster electronics will at least get up to what Canon sees as the normal number of MP for FF - low 20's.
As for what is restricting 14 fps raw, quite obviously that sensor gives the read out just fine, the A/D circuitry works, and its processing system can take the input and convert it. Could it simply be the write speed of the buffer isn't up to taking the data at the rate needed for 14 fps in raw format?
Or could it be as simple as Nikon's 14 bit raw dropping to 12 bit raw at higher frame rates on certain cameras? Possibly Canon didn't want to drop down from 14 bit raw, so they just did a quick and dirty solution of limiting it to jpeg only? 14 bit at 12 fps vs 12 bit at 14 fps... If that's the case, 12fps 14 bit raw is the absolute limit of its processing speed, not just the buffer.