As stated above, I was using Minolta for 35mm film needs until better quality AF was necessary. As a result, I was already switching an entire system and didn't suffer what I recall was a traumatic change of lens mount for Canon users desiring AF bodies. In short, they were royally pissed off. They had to replace all their glass, too (I think). Again, trying to recall something that wasn't of immediate importance to me, didn't Nikon maintain the same mount?
The reason I bring that up is, Canon has already made - yet again - an entirely different mount for their mirrorless bodies. If they're going to concentrate more R&D on mirrorless, does that mean a decrease in DSLR development? If so, do they bridge the mount gap for existing clients? What about EVF? I have yet to look through one of those that feels natural, though I haven't yet handled a Sony a7RII. I hear their EVF is impressive.
On balance, I can probably play out my career on the 5D3 and 7D2 I own currently, but that's not true for a lot of people who will feel the pressure to switch, for whatever reason, probably within 5 years. The profitability for photographers goes down as the price of keeping up technologically goes up. Of course, the camera manufacturers mostly have healthy margins. It used to be you kept the same body for decades and bought new glass. The improvements were in the film, an expendable commodity you bought as needed, thus a greater percentage of the profits stayed with photographers. Now the cameras are the expendable commodity.