..."there is some internal discussion about what to do with the EOS M line of cameras and lenses."
In my view, there is more than a bit of 'anti-M' bias here on CanonRumors (one of my favorite websites)...at times I even think I see this bias from people who post A LOT here.
Canon's executives and technical people will always have some internal discussion about what to do with the M line...I hope they continue to have those discussions for a long time.
They could be having discussions on how to get 'better' (as in more high-performance) sensors inside of an M.
I own a 5D Mk III and two Canon APS-C DSLRs...as well as Canon-branded wide-angle zooms, 2.0 and 2.8 and 4.0 primes...and telephoto zooms.
There is a place for a large body that two large hands can nicely hold...with a heavy telephoto lens attached...and an ultra-modern focusing system that enables birding etc...with a modern sensor inside...a sensor that also excels in low-light situations.
There is also a place for a large body that has a sensor with zillions of pixels inside...for situations where a tripod is often critical (landscapes and architecture/real estate).
And then there are also places for the M format, which, for the money, in every way except for sensor performance, when combined with the EF-M lenses...supplies a superior experience for those who want to acquire high-quality images...sometimes WHILE DOING OTHER THINGS (can you say family vacations and pictures around the house?)!
And what some people overlook is how (relatively) inexpensive the M5 and M6 are, when kitted with the 18-150mm lens (compared to the gold standard of the OM-D E-M1 Mark II/Olympus 12-100mm lens duo).
A quick search reveals a difference that approaches 2K USD!?
I envision a long lifetime for the M format, and for the EF-M lenses, all of which have the same diameter.
And yes, with an inexpensive adapter, all of the lenses purchased for the EF and EF-S formats work perfectly on every M I've used.
With sensor development, the M will continue to be the smallest and in some ways the BEST APS-C-sized sensor camera on the market.