This goes without saying...
Canon's processors are not known to be the most powerful or speedy chips out there, this is why (well partly) that there are so many limitations with video shooting.
Canon needs multicore CPU's or simply double up like on the 1DX II. I think we will definitely be seeing more than one CPU in any mirrorless that has real video specs and/or high speed stills capture.
I can't seem to find it but I'm pretty sure some site mentioned that Canon was setting up a new production line for their processors that can produce a much smaller die. Right now the digic 8 processors are somewhere around a 35-40nm process. Most new phones use somewhere around a 10nm process, and most 'cheap' phones using previous years processes are still around 23nm or smaller.
Just shrinking the die means they can put twice as many transistors in the same amount of space, or they can choose to just keep the number the same and have less power consumption and greater speed. A combination of the two could lead to some very speedy digic processors.
However the size of the actual sensor is hard to shrink at this point, because of the physics of light. That's why stacking the processors can be so effective, as the signal can travel backwards to a corresponding set of transistors to do initial processing rather than through a trace all the way to the edge of the board before being handed off to those transistors. (this is different than Foveon's use of the term 'stacked', where they actually stack the sensors themselves to capture more light).
I'd lean towards a 1dx style camera in 1st quarter with dual digic or a new die-shrunk digic 9. I hope we will see one of their new stacked sensors in production soon though because that opens the door to 4k/8k 120fps. Right now they can't do that because of the heat and bandwidth. Smaller processes for the stacked portion of the die and external digics mean more bandwidth + less power which equals less heat.