Just for the fun of it, this is what I think will happen.
Canon will release the FF mirrorless with a new mount. Why? Because Canon works on segmentation. This makes sense on many levels;
They will deprecate the EF-S mount- they will stop developing EF-S lenses and they will only continue the 7D, Rebel, SL lines if it makes sense. Reason? EF-M is the new APS-C representative.
The new mount - let's call it EF-X here - will co-exist with the EF. Canon will initially focus on enthusiasts, fashion and wedding photographers, where the photographer benefits the most from being able to see what the picture is going to look like without chimping.
Professionals who use the 1DX will be expected to stay there. Those who want to use the new camera, for greater FPS will have to use the adapter. Likely lenses for the new camera will be 24-70, 50 and 85mm. 70-200 will come later.
I don't think that they intend to develop a new sensor. They will use either the 5D or 5DSR sensor.