I jus noticed this schematic of the
Canon RF 85mm f/1.2 and a couple of things are surprising or interesing to me.
Firstly, even at this long a focal length — more than twice as great as the depth of the Canon EF mount — there is apparently a design advantage to having elements right at the back of the lens body, far closer to the focal plane than any 35mm format SLR lens mount allows. So it seems that getting rid of the mirror benefits a wider range of of focal lengths than I expected, at least for very bright lenses like this f/1.2 and Nikon's 58mm f/0.95.
Secondly the rear elements occupy almost the full width of the mount, which is also true for the 58/0.95 Z, so some lens designs do indeed benefit from a wide throat; wider than Sony E-mount, it appears. Still probably only true for a few extremely bright "statement" lenses like these though.