I keep reading a whole bunch of reasons why Canon "should" switch to a Sony sensor for more DR, but I have yet to read one response that needs to be brought up:
In-house engineering expertise.
This is something I've thought about. As a manager myself, I wonder to what extent Canon management is concerned about the morale of their engineering and manufacturing divisions is they started buying sensors from a competitor, as many on this forum have suggested.
First of all, let's say for the sake of argument that Sony sensors really are better at this point in time (a judgment that is highly subjective and very suspect, since it hinges on tiny, tiny differences in just one subset of a sensor's overall performance, but that horse has been so thoroughly beaten, let's dispense with it for now)
What would it say to Canon's employees if the management team said, "sorry guys, you've done a good job but we decided to buy sensors from Sony because they are slightly better in one category that hasn't affected our sales in the slightest but it's caused a handful of people to go crazy on the internet."
It seems like the first impact would be a rush to the door by the most talented persons. They've spent countless hours perfecting products and now the management is saying, "sorry your best isn't good enough."
Who knows what would happen next? Maybe quality control would drop and Canon would ship out a bunch of cameras with sensors that have a serious oil leak on them and be forced to replace the model early and offer customers a free replacement at substantial loss to the company.
I don't know. Could such a thing happen?
Perhaps Canon, being a conservative company, figures: "well, these small differences are not affecting our sales. It's more a case of bragging rights. No one knows better than our own engineering team where we have to improve. They've done a great job innovating for us in recent years, let's hang in there with them for awhile and see what they come up with because we know they are pushing themselves harder than we ever could."