The bottom line is that mirrorless will remain a niche at least in the USA. Professionals want the best quality and best ergonomics, while consumers want the best deal and best practicality. Mirrorless fits neither of those formulas, thus it is doomed to third tier niche status that may retain a devoted fanbase but will never make it beyond that. The very best scenario for mirrorless advocates is a hybrid camera (as an optional EVF mode to augment a traditional OVF viewfinder), but based on the anemic mirrorless sales it appears that will not be a necessary investment for any of the big players.
Let me put the situation to you differently.
If tomorrow Canon came out with a 5DIV and a EOS-MX, where both were full frame and using the same senor but the MX was mirrorless (with corresponding weight savings, etc), I'd buy the MX in a heart beat and never even consider the 5DIV. I'd also never buy another EF lens that was for non-mirrorless cameras.
The size and weight differences are not inconsequential and if I think to the future then at some point I'm going to say "I'm sick of lugging around fat ass DSLR bodies and lenses when I can use something smaller and lighter." If I buy another DSLR it will either be the last or next to last DSLR that I ever buy.
Now maybe that's further into your future than you care to think about but not for me. In 30 or 40 years, what do you want to have hanging around YOUR neck?
I think DSLR an mirrorless cams will coexist at least 2 decades as an offer of the large camera brands. The whole live is a large heap of compromises and sometimes there is no logical OR but an AND:
DSLR: Action, "looking throu cam to check subjects without power consumption", etc.
mirrorless: If lower weight is important, tripod work, etc.