My guesstimate for mirrorless to overtake DSLR is < 5 years.
+1 After 60+ years, in 35mm body development, the OVF is about as good as it will ever get. The EVF can and will improve with the advance of technology. The current Z mount bodies are high end consumer grade (IMHO). Once Nikon and Canon commit to releasing Pro quality mirrorless bodies, the market for DSLRs will collapse.
When using AF, no matter how sharp your lens is, if you cannot put AF sensors on the subject, your images are likely to be useless. More image sensor coverage by the AF system has multiple advantages. Having 93%+ coverage means that you can nail the grab shot where there isn't time to "focus and recompose". The best high-ISO sensor in the world does you little good if you cannot see the subjects and/or focus on them accurately. As demonstrated in the first video, being able to clearly see your subjects in the dark, means you can compose and use AF or manual focus (if necessary), to focus on the subject more accurately.
As they became available, I rented the D5, D500, and D850, to shoot paid gigs of Land Speed Racing Events before I bought the body that worked best for my needs and style of shooting. The D850 allowed me to shoot FX for cars and DX crop for motorcycles, with plenty of resolution in both modes, so it was better than the D5 or D500 in image size versatility, but like the D5, AF coverage area was FX limited. As many advantages as the D5 and D850 had over the D500, neither had as much AF sensor coverage of the image area, which is very important to me. Having shot the D500 and D850 side-by-side at one motorsports gig, it was clear to me that although it and the D5 were great cameras, their distant subject magnification in the viewfinder paled in comparison to that of the D500. Given the greater AF sensor coverage and better viewfinder image for distant subjects, the D500 was the body to buy for my needs.
The D850 and D5 both have DX crop modes, but that only masks the view to a smaller portion of the viewfinder image. Had the D850 used an EVF like the Z7, the potential for the viewfinder DX image area to be zoomed in in-camera would have made it the superior choice to the fixed view of the D500. With an EVF one can see the DOF and exposure real-time in the viewfinder, plus take advantage of a far greater AF coverage. Add the the potential of "in the EVF" zoom and low-light enhancement, and mirrorless will eventually replace the static OVF everywhere. The Z6/Z7 are not pro level yet, but it is just a matter of time....