One of the new RF lenses already announced is the 24-240mm f/4-6.3 IS USM, so they've already broken the old 'no -f/6.3 zooms' rule.
Also the Canon EF-M 18-150mm, which is already out.
AND the Canon EF-M 15-45mm STM IS, which is also f/6.3 at the 'long' end (45mm).
I own the EF-M 15-45mm lens, as well as the EF-M 18-150mm lens (horses for courses).
I also owned the Canon EF-M 18-55mm STM IS, which is f/5.6 at the 'long end' (55mm)
On both my M5 and my M10, there is/was no noticeable difference in focusing speed between f/5.6 and f/6.3
(I owned all 3 of these EF-M zoom lenses at the same time)
On the other hand, the EF-M 22mm f/2 lens focuses notably better in low light / lower contrast situations than any EF-M lens at f/5.6 or f/6.3.
Bright prime EF and EF-S lenses all focus better in low light / lower contrast subjects than the EF-M f/5.6 or f/6.3 lenses.
(I'm talking about lenses such as my EF 50mm f/1.8, the EF 100mm f/2.8 L and EF-S 24mm f/2.8 with the EF-to-EF-M adapter on my M5 and M10).
So there's a lot to say for having 'a bright lens', even though Canon's Dual Pixel Auto Focus (DPAF) is good in regard to AF.
Having said that, the EOS R and EOS RP have better low light focusing ability than the M5 (or M10).
Additionally, I remain impressed how well the
non DPAF M10 actually focuses.
I do hope Canon's next iterations of DPAF will be even more powerful, and allow potentially better focus in low light with 'dimmer' lenses.
That, combined with a really nice, long Canon telephoto zoom in RF mount,
and a more pro EOS RF mount FF body, would certainly tempt me to more seriously branching into Canon's FF mirrorless line.
The possibility of
Quad Pixel Auto Focus (QPAF) with the ability to pick up both horizontal lines and vertical lines well is also alluring....