So as it turns out, Sony is willing to sell some of their sensors:
Sony sensors can be found in cameras from several different manufacturers. How does your sensor business work?
When we make sensors we put them in several categories. [At any given time] one category of sensors is reserved purely for Sony cameras - we don’t sell them to other companies. Like the sensor in the A7S. But once we’ve enjoyed this advantage we might sell them on later, after some time has passed. This is the second category. The third category of sensors is completely generic - the sensors are created for use internally and to sell externally, to anybody. China or Taiwan or wherever.
and Canon does not discard to buy them:
Canon released two cameras at Photokina - the EOS 7D Mark II and PowerShot G7X. One thing we’ve learned is that the sensor in the G7X is not made by Canon. Does this represent a new philosophy at Canon?
We select the best sensor, whoever the manufacturer is. That’s our policy.
So, let us imagine that Canon releases a 5D mark IV with the 36MP pixels sensor from the D800 and the A7r. Let us suppose that Sony supplies the same slightly improved sensor to both Canon and Nikon for the next 2 generations of cameras. Then, suddenly, when both vendors are addicted to Sony's sensors and have almost completely dropped their R&D in sensor technology, Sony releases a killer 100MP sensor with zero noise at ISO 51200 and 24 stops of DR and decides not to sell it to any external vendor. Sony would absolutely take over the market!
Definitely, it looks like a good decision for Canon not to use Sony's sensors for their flagship cameras. But, don't you think that Nikon is already in Sony's hands?
It would be poor for me, since the Sony DR is weaker at the high ISO's I use. The advantage at low ISO's is noticeable with poor lighting or poor exposures, but not ordinary images. I'd like to have my cake and eat it too, but, for now, its a tradeoff. If you use mostly ISO 100, or mostly ISO 3200 and above.
Sony could indeed take over the market if they could defy the laws of physics, imagine how they could take over the world with a perpetual motion machine. Basing a theory on things that are not going to happen because they are physically impossible is nonsense.
BTW, Canon has been using Sony Sensors in many of their cameras since their first digital camera, its only when they went to CMOS, and Sony did not make CMOS sensors that Canon started using them.