Apologies, but I just read the first post and tl;dr the whole thread.
Short answer: yes. Reason: IQ.
What, you ask, does SLR vs mirrorless have to do with IQ?
Just google for "3chip camera." Bayer filters currently filter about 2/3 of all incident light. A mirrorless pro-level camera with a 3chip design would allow closer to 100% of incident light to be used, and without the other problems introduced by the Bayer pattern (sharpness). I.e., would you rather have a 36MP camera with a Bayer pattern, or a 24MP camera with 3 individual color sensors, and three times the light absorption? (Yes, of course I pulled those MP numbers out of the air, but it's got to be cheaper to build three lower-density sensors, without Bayer or AA filter, than a single higher-density sensor with Bayer and AA.)
As soon as manufacturers find a way to make an EVF fast and accurate enough for pros there will be no reason to stick with SLR's, and they should be left in the gutters of history.
Besides, when I take a picture I don't want to see the world the way it really is, I want to see it the way my camera sees it.