For APS-C sensor, M mount makes more sense. Look at the existing M system now, it is as compact as it can be. It can use practically ANY lens that has ever made since 1930’s with the proper adapter. That cannot be said with the RF mount. Also the RF lenses are HUGE compare to the M lenses. If Canon put his mind into it, they can come up with M lenses as good as L lenses. There is no reason why Canon cannot have two mirrorless lenses lines. They are doing it now.