Seeing as the M200 and M6 Mark II were released last year, its only natural for an M50 Mark II and M5 Mark II to be the next ones. The M6 Mark II moved up quite a bit in performance vs. the original M6 (which was an upgrade from the M3). As such, it seems Canon will be giving an "R5 like" treatment to the M line with the M5 Mark II. Features like 5-Axis IBIS, weather sealing, and duel card slots are all possible for the M5 Mark II, along with a bump in shoot-to-shoot performance.
To address the gap with
EF-M and RF lenses, Canon may release an adapter along side the M5 Mark II to allow RF lenses to work on an M series camera. Granted, its been discussed heavily that a simple
EF-M to RF adapter like the current
EF-M to EF adapter is not physically possible due to the very small 2 mm difference between
EF-M and RF mount flange distance. Though that doesn't rule out an
EF-M to RF adapter with lenses elements to refocus RF lenses onto the smaller APS-C sensor from a further flange distance (sort of like current speadbooster adapters).
If Canon is to continue the M series cameras along side the RF series, then the mount gap needs to be addressed by Canon for this to make sense. Example: The RF 24-105 F/4 L lens is superior to the EF 24-105 F/4 L II lens. Does it make sense for an M series user to buy the EF version to adapt to there camera now, then have to sell off everything if/when they decide to go to a full frame RF camera? Yes, they could adapt that EF 24-105 F/4 L II lens to an RF camera, but does that really make sense? Wouldn't someone buying a lens as expensive as an L lens want the RF version with better performance and features?