Here's a different way to think about the Canon and Nikon announcements last week (1DX m3 and D780): they're mirrorless cameras without an EVF.
The Nikon D780, for instance, is essentially a Z6, but with a mirror box and an optical viewfinder as the primary compositional path. Put it in Live View, and shooting via the rear LCD on the D780 is essentially the same as shooting with a Z6.
Meanwhile, the Canon 1DX m3 is not really different. It's essentially a form of a Canon RF camera, but with a mirror box and an optical viewfinder as the primary compositional path. Unlike the D780, the 1DX m3 has a number of serious refinements on the DSLR side, but when you put it in Live View and shoot via the rear LCD, the 1DX m3 essentially becomes the same as some currently non-existent RF mount mirrorless camera.
This is true for both cameras in both still shooting and video recording modes. Indeed, the D780 gets virtually all the Z6 video goodies, including 10-bit N-Log HLG on the HDMI port, while the 1DX m3 actually goes further than Canon has before with their mirrorless, adding 4K/60P and 5.4K raw. Yet, operationally, these DSLRs work pretty much exactly like their mirrorless counterparts when you shoot video.
All this makes you wonder: why didn't they just put in a flip down (or up or across) EVF in the viewfinder that activates when you press the Live View button? That would not be even close to technically impossible, though it might grow the prism area in size. Alternatively, use an OLED overlay system, though that would require some engineering that hasn't been done before.
The real question I have is this: was making DSLRs into EVF-less mirrorless cameras just a result of so much energy being focused on the mirrorless side of development these days, or is there really an opportunity for a hybrid, best-of-both-worlds camera in the future?
That's a question we may have to wait another four years to know the answer to, it appears. Why four years? Because a good hybrid mechanism is going to be expensive to develop, thus it would likely only appear on the top end DSLR first, which means a 1DX m4 or D7 that would show up just before the 2024 Paris Olympics.
But here's the problem: the still strongly declining camera sales are likely focusing the remaining R&D budgets away from the DSLR. Canon and Nikon have to clip Sony's wings or else suffer even more than they otherwise would from market contraction, and DSLRs aren't going to do that, no matter how good they are.
As I pointed out over a decade ago, mirrorless was inevitable for the bulk of camera sales for one simple reason: parts reduction. That parts reduction also leads to manufacturing simplification and more assembly automation. Faster, simpler assembly with fewer parts leads to lower overall product cost (to the manufacturer) and potentially higher gross profit margin. (The same thing is going to happen in automobiles, by the way: they'll move to electric not just because of global warming concerns, but because it results in a parts reduction and less manufacturing complication.)