The main advantage of the new mount is the shorter flange distance, but I would probably use old EF lenses anyway instead of buying expensive RF glass. That would negate the advantage of the new mount though.
Flange distance is not always an advantage.
It offers no advantage for super telephoto primes and leads to vignetting on wide-angle lenses.
The bigger advantage to mirrorless is being able to autofocus at lower apertures.
There could not really be an EF 100-400 f/5.6-8, EF 600 f/11, EF 800 f/11, or EF 1200 f/8.
Of course, those are not the most suitable lenses for skyscrapers.
I am not sure if Canon will ever make another super telephoto zoom since they seem to be going the zoom route but if they do then I think they should continue to make an EF version and just have a separate RF version with the same optical formula and same focus motors.
I actually think they should do the same thing for wide-angle lenses.
If anything, I think Canon should still come out with DO super telephoto primes like the EF 400 f/4.
Nothing against the 600 f/11 and 800 f/11 but those are not weather sealed.