A light and compact 100-400 would be welcomed by many M users. The light EF alternatives kind of end at 300mm and the Tamron 18-400 doesn't like M cameras much (i.e. Tamron won't even try to make the AF work correctly for an M body), plus it is on the heavy side. Other than that, yes a replacement for the M5 would be nice, but I suspect the technology is not quite there yet to fit some of the new processor features into the M power envelope. The fact that the M6 II didn't include the nice downscaling 4k crop mode video feature of the 90D was likely due to power limitations. Clearly, the AF and video features of the R5 and R6 (i.e. digic x) are pretty power hungry, so maybe we are just in a bit too much of a hurry. Only time will tell. BTW, since it uses the same battery, a more competent replacement for the RP suffers from the same power limitations as the M cameras.Given Canon has discontinued some EF lenses, it is unlikely that they will release a new EF lens in the future. RF needs more lenses and Canon wants users to migrate as soon as possible. Note that RF lenses offer something additional to their EF counterparts to justify their higher price in most cases eg weight/size/aperture/focus speed/magnification/focal length etc. If we combine RF and EF, there is an amazing range of lenses available.
Is there a need for a new M lens? They seem to have a complete system and you can always use a EF-s/EF lens especially for telephoto.
A new M body would be welcomed.