I own the Canon M5 with a bunch of lenses, including Canon's 22mm f/2, 15-45mm, 18-150mm and the Samyang 12mm f/2.
From a 'throw in my bag and take along' perspective, I love the size and compactness, particularly the 22mm as a prime or the 15-45mm as a zoom.
The ergonomics work pretty well considering what it is, and particularly that I do not use my M5 with any large lenses.
My main cameras for over 15 years have been DSLRs. Currently the 80D is a very versatile all round APS-C model. I have many EF and EF-S lenses... but all of them (on any DSLR body) are significantly larger than the M5 with equivalent lenses.
I used to own the M10 - which was really nice and compact without the viewfinder / hump. However from a usability perspective, a camera with just a rear screen is almost as frustrating for me as using a smart phone - both in terms of ergonomics (holding out from body) as well as . Hence I gave that (and a spare 22mm f/2 I bought 2nd hand) to my nieces.
The fact that I have a good astrocombination with the Samyang 12mm f/2 AND the portability are the main reasons I see me staying with the Canon M series into the future. I like portability, but along with an EVF.
So a M5mkII would be particularly attractive to me. It fits the gap between a FF mirrorless (or DSLR) and my smart phone. Image quality of the M series is great, while still being compact and portable. The M6mkII indicated how serious Canon remain with their M series, it has some great features - and I hope the M5mkII includes all of the goodies from the M6mkii, as well as a few more (e.g. IBIS) .
I expect I will buy the R5 camera if the 'as-yet-unknown' feature and functionality (AF, IQ) are like I expect they will be. So I'll probably maintain a 3 tier system:
1) FF mirrorless (for the majority of my photography and videography) - with great IQ and 'all day ergonomics'
2) APS-C mirrorless (for when I am going out and require a more portable package, to still have very good image quality)
3) smart phone (for when I am just taking unplanned 'quick photos and videos on the go' (as my smart phone is always with me) .
It'll be interesting to see what Canon is going to provide in the next little while, in terms of my tiers 1) and 2) above. No concrete details have yet been revealed about a possible M5 replacement. I would love an M5mkII with faster AF (particularly in low light), a higher resolution (and faster updating) EVF and IBIS being the top items on my wish-list.