I'm vocally predicting death of SLRs soon (or at least FF), but to be clear I don't have an emotional investment in that. I'm not on "Team Mirrorless." I just haven't heard any possible advantage to SLRs except battery life and especially when you have long viewing times per exposure (wildlife).
So curious, do you have any particular reasons to think "high-end DSLR will hang around for some photography pros for quite some time?"
Also, I think the 5-10 years you mention may be much closer to 5, albeit counting from when there is a pro MILFF, trinity zooms + superwide + portrait available. I think take-up of the RF system hasn't even begun yet. I don't think the FD user base lasted 3 years once EF trinity zooms were out (and 50/1.4, 35/2). In fact not even Nikon lasted 3 years after EF system's initial trinity zooms were out.
Yes, because--
A) Judging by the resistance to change displayed by some on this forum, some of whom I assume must be photography pros, there will be some people who will remain skeptical of smaller, lighter, newer gear. In other words, change is hard and a lot of people are fearful of it.
B) DSLRs just feel like more solid gear, even though this is actually not the case (more moving parts, etc.). But they are generally rugged and heavy and do have a reassuring feel for those that use them. Better ergonomics for those with large hands, etc. (no Trump jokes, please).
C) Perhaps there will be a resurgence (much as there is for 35mm film SLRs these days) and people will start buying used DSLRs on eBay as a novelty. These won't be pros, but could be one reason they hang around.
D) Also, clients tend to sometimes perceive bigger cameras as more professional, even they are incorrect in this day and age to do so.
Anyway, these are a few reasons, maybe none of them good, but I agree with you; once pro MILFF with the corresponding zooms are out and as the ecosystems grow for both Nikon and Canon, things will speed up rapidly.