There have been a few posts after my earlier contribution, where I shared my experience of having and using Canon's M5.
A few observations to note and aspects to share (very conscious from my own perspective):
1) Ergonomics is very subjective. Based on many factors, including handsize, preferences, other physical characteristics, etc. What works for one, may not necessarily work for another. I have average size male hands (for a middle aged Caucasian male).
2) Some people learn / adapt and are both better & quicker at developing muscle memory than others. I have used film cameras, then early model Fuji and Kodak digital P&S. Then Canon DSLRs, and added Canon mirrorless to the mix. I have adapted to each.
3) I believe I will always feel that a camera the size of around my Canon 80D is more of a natural fit than a M5. a bit smaller than the 80D could work, and slightly larger also (e.g. I also own the 7D which is notably larger / heavier, but still comfortable... and I really appreciate the thumb joystick)
4) In terms of ergonomics, the 80D is a significant step up from my Canon 350D. The 350D's grip in particular is frustratingly cramped. But the 350D still feels way better than most P&S cameras. The M5 is a step up from my M10. The lack of any real grip on the M10 is a shame, but understandable. Plus it keeps the camera / lens combination small and light. However the M5 with a compact lens (e.g. 22mm f/2 or 15-45mm zoom) is very portable and light.
5) The Canon M mirrorless bodies DO fit a specific niche / area, e.g. with the smaller / more compact / lighter lenses. I do not intend to use my current mirrorless cameras (M5 or M10) with larger EF/EF-S lenses much at all, i.e. via the adapter. I rather use my DSLRs (mainly 80D and 7D) for larger lenses e.g. my 70-300mm L, my 100mm L, Sigma 8-16mm or my 15-85mm lens.
6) I hope that Canon might produce one (or more) EOS-M (mirrorless) APS-C models, which are a larger camera body- e.g. somewhere in the size range of the 800D / 77D / 80D. I also hope that Canon's FF mirrorless will incorporate a lot of great existing technology (e.g. DPAF) with some potential improvements (e.g. improved battery life, improved initial acquisition and tracking, low-light work)
7) Lenses! The existing APS-C EOM lenses are great quality - in terms of image quality and size/weight/build quality. The existing lenses are very good in terms of IQ (sharpness, contrast, IS, AF speed and accuracy). I would look forward to some new/more lenses soon (obviously also those more suited to FF too).
8) Canon is smart. Their market share and history demonstrates that. Canon will likely produce a solidly producing FF mirrorless camera with reliable and very well implemented feature, that will sell well and be used by many happy photographers and videographers.
Regards,
PJ