I can see mirrorless driving improvements in dslr liveview, which is a good thing.
I don't know if this is possible, but if you put a miniature display into a dslr viewfinder that works when mirror is up then you get a dslr that can work as a modern mirrorless. Combine it with a shutterless sensor (when Sony make them) and you get a very versatile camera without changing much mechanically.
SLR cameras were a solution to a problem that today doesn't exist.
"How to use a single lens both to view and frame the shot and expose the imaging medium to the image at the appropriate time."
It was (and is) an elegant solution, and we've had around 100 years of investment to make that solution the very best it can be.
Fast electronic sensors and fast electronic displays (as well as a few other things) remove the problem - there is no longer a need to optically split the path, when you can do it electronically. Slow sensors and slow displays were not up to the task, so the DSLR was born, but latterly, we are at the cusp of this breakthrough.
Removing the mirror also removes some of the challenges associated with it - it's not just size, and speed of moving the thing around, it's having to maintain and calibrate two different optical paths (micro adjustment of lenses etc).
I really don't see any further significant investment into mainstream DSLRs going forward. There may be one or two more major releases, but the investment will surely be into Mirrorless, and those releases will be driven by exploiting the technology of mirrorless in a DSLR rather than enhancing the DSLR itself I feel.
That said, there is still a gulf between the legacy lens development of 100+ years on SLR format, so I don't see anything stopping DSLRs still selling well.