Ok, let's see things in a different way.
EF lenses line-ups are due to end anyway, may it be EF, EF-S or EF-M.
So no problem if Canon ends the production of M system for EF.
But I think they may reconsider keeping the -S concept first. I think it's clearly a dead end (and I hope they won't maintain all those useless numerous 18-xxx either BTW).
To my sense, the future APS-C line-ups should only be of two kinds :
- high-end for prosumers sport/wildlife (i.e. EOS R7 or any 7D replacement), in other words, products for customers that mainly use FF lenses on APS-C to have more reach.
- "Mini" for travel, family, VLOG and any casual usage (i.e EOS M... ), in other words, products for people that dig nice little "gems", like EOS M cameras actually are, for their every day life (which old EF-S, Rebels etc. tend not to be, if ever they were considered that way...).
These may be the only two "cropped" line-ups that have still a chance to be sold enough in the future.
But IMHO, they need to enhance EF-M to RF-M to make it more competitive in the APS-C mirrorless market (and I think the only adapter still needed would be the RF-M to EF considering the number of EF lenses around vs RF Lenses for the moment... that and the fact most EF-M owners love much more having lenses made to fit the size of the camera, may they be third party or brand name).
So, yes, EF-M "must" probably die, as all others EF mounts... but still, it should perdure thru another, more modern type of mount.