Okay, here's what I have now:
20D/5D - semi-retired
7D Mark II
8-15/4L fisheye (180° horizontal to 22mm-equivalent rectilinear when defished)
10-18STM (lightweight rectilinear ultrawide with IS)
Sigma 18-35/1.8 (standard for low-light moving subjects)
18-135 nano-USM (good light general walkaround and power-zoom semi-hyperzoom for video)
50/1.8 STM (low-light gap-filler)
55-250 STM (light-weight stabilized telephoto)
70-200/2.8L IS II (low-light stabilized telephoto)
Sigma 150-600C (good light super-telephoto zoom)
Celestron Edge HD 11 with EF adapter (2,800mm f10, 2000mm, f7 with wide adapter)
To switch to a full-frame R, I figure:
Keep the 8-15 and always use it in crop mode (I have no interest in circular fisheye shots).
Replace 10-18 with 15-35/2.8 ($2,300) (similar range, faster, heavier and way, way more expensive)
Replace 18-35/1.8 with 24-70/2.8 ($2,300) (tiny bit more range, same speed, stabilized)
Replace 18-135 with 24-240 ($900) (tiny bit more range)
No replacement for the 55-250 (no lightweight 400mm-equivalent lenses are available)
I guess keep the 70-200 and 150-600, and just take the resolution hit (17MP vs 20MP in crop mode), or replace the 70-200 with the RF 70-200 ($2,700)
Use two adapters (RF-EF, EF-2 inch) with the scope.
So, that's $5,500 + the body or maybe $8,200 + the body if I replace the 70-200 as well, minus anything I could get on the used market. Add to that, a half-dozen batteries since the battery life is bound to be half to a tenth, depending on what you are doing (I have three batteries for the 7D II now).
What would I get for that? Well, I'd have a lot more speed below 29mm-equivalent due to the 15-35 and 24-70, and a bit more range in the walk-around (24-240 vs 29-216, while having less resolution in the fisheye and at 600mm on the 150-600. And I'd have to deal with a likely far-inferior viewfinder experience that would make it much harder to track high-speed subjects, which is a good 90% of what I shoot. But the alternative is I basically keep what I have forever because no upgrade will ever happen.
Doesn't sound like there are many decent options for me.