I think this is why we will see a big shift to mirrorless by Canon and Nikon. DSLRs have pretty much reached the end of the line in terms of big advances. No more leaps forward in frame rate or AF, just incremental improvements. This is not to say mirrorless are clearly better than DSLRs, as there are pluses and minuses for both. Just that the manufacturers can no longer include leaps forward, and the only thing moving forward which will make a difference to photographers, are sensors, which are equal with mirrorless. Whereas potentially mirrorless has some way to advance in terms of frame rate, AF, EVF performance. In other words, what I'm saying is that new performance camera i.e. in the class of the 1Dx or 7D line in DSLR form would have similar AF and frame rate, but a new mirrorless equivalent could have a potentially much higher frame rate and more advanced AF system.
My comments are purely based on manufacturers marketing these products. Certainly the manufacturers are capable of producing more polished DSLRs, just not a leap forward in performance. I think this is why we never saw a 7D mkII update yet. Canon would struggle to produce anything more than an incremental and more polished upgrade, with sensor resolution being the only possible leap forward. Yes, there's a number of things which could be updated, deeper buffer, better video specs, but overall camera performance will be similar.