I think the comments about the market for the 7dII drying up or being too small might be on the money, but in a different way. I think the majority of the 7d users wanted accurate focusing at high speeds. The dual card slots and weatherproof housing was a bonus for the majority of the users, but not critical.
The new m6II has shown that the baseline experience with the new Canon sensors can hit 14fps with very good focus tracking, and with a greater focus on electronics and firmware within the camera the m6II has given us a sneak peak at what could be done with a much higher MP count full frame body when it's cropped down for speed.
I've always thought that there were two different classes of people who invested in the 7d series:
1) Birders and sports photographers who need the crop factor to put maximum pixels on subjects that are far away and difficult to focus on.This group of people is much more likely to invest in high end (3k+) lenses. The reason the 1dx is not used is mostly because of pixels on target, and not as much because of money. This is also the group more likely to have a critical need for weatherproofing. This is also a much much smaller % of buyers.
2) Prosumers comprise most of this group, and are primarily people who wanted something that can focus well on fast moving subjects and have fast fps, but are generally not using anything bigger than a 70-200 or maybe a 100-400.
The number 1's can afford a more expensive full frame camera that can be used as full frame when needed, but can have much higher speeds when used as a crop with the same amount of pixels on target that APS-C could do. That camera will have the dual cards, ibis and weather sealing expected for that class of camera.
The people in group #2 are way more price sensitive, and many of them had already bled off to the 80d (and presumably 90d). The ones who are left who are more concerned with fast accurate focus will be able to jump into the next generation R or RP in a few years. Some of them could jump into the m6ii now. I imagine full frame R or RP will be in the 8-10 FPS with full tracking by the time they come out. And there's still a chance that Canon might release a 90d level of r-mount aps-c. If that happens, they add a bit more buffer to the internals used in the m6ii and they've hit the 7diii speeds and focus.