I just don't see them using the full frame sensor(you'd have line skipping problems again), for a video camera @ $3k , so how are they gonna use a smaller sensor and still call it a 5D?. It doesn't make any sense. They need to differentiate from their existing cameras (by pricing above probably). This means a new lineup.
The problem is we don't know what the boffins in their white coats have been cooking up in the labs.
If you watch the video the rep mentions a few times that the 1DX is a PRO Photography DSLR camera, the video was extra.
He makes that point clear a few times.
This is why it sounds to me like they are going to try and release a PRO Video DSLR e.g. the next 5D model being that its been accepted unofficially by the industry as being the video DSLR of choice already.
You mention line skipping but as they said in the video that it has been reduced dramatically with the new sensor, remember that this is the Photo DSLR, it then makes me wonder what the Video version could achieve.
As for the smaller sensor, If you are shooting video @1080p you are pretty much using about 2MP, so increase that to 4K (4096×2160) and you will be around the 8.8MP mark.
The current 5D2 shoots Photos at 5616 x 3744 as we know is 21MP. even if that was reduced to 18MP like on the 1DX it can still more than cover the sensor range required for 4K.
Sure you may loose 3MP but you also gain a clearer image with better spacial resolution.
Think of it more like the CPU race that happened a few years ago, people were pushing for faster and faster CPUs, until we hit almost 4GHz, then suddenly the average CPU dropped to around the 2GHz speed. BUT they also added a second core, then quad core, octo core etc.
By reducing the speed of the core and making it do more with the cycles it has they managed to create much more productive CPUs.
If we then take that same analogy to camera sensors it seems that Canon are doing the similar thing now. Reduce the MP count but make the pixels that are there do a hell of a lot more.
If this means that we get much better quality images (even if slightly smaller in physical size) then that doesn't seem like an all too bad thing, especially when you can then blow the image up with less distortion.