I'm curious too, the 80D is only 3 years old, and it's not lacking much (other than possibly 4K). Give it a resolution bump, maybe the better AF system from the 7d Mk II, I'm not even sure what else. A few FPS?
The 7d mark ii is 4.5 years old, I wonder if there still is a chance that these lines get merged?
For it to retail at the same price as the RP, it'll definitely need a few major updates. 4k the bare minimum (and with no DPAF or crop limitations), the competitors all do 1080/120 too, but I doubt Canon matches that. AF system will need more points and a better spread. Probably need to bump the normal and burst FPS by at least 1 if not 2 shots per second.
But you're sort of getting at why the XXD line probably isnt long for this world. While its a great start-out all rounder, it just cant compete spec-wise with say, an a6400...which is gonna double a 90D's frame rate, 10x its AF points, and include things like eye-AF, at 70% the price. A new 7DIII would, but would die at a retail price of $1799 or so for anyone but pros.
In a way, it makes more sense to keep selling 80D's at something like $899 for a while. Because there's no sign that the sensor tech, iso performance, etc is gonna take any major leap forward any time soon to really justify a new version.