If I may make my own response to Jake's query about the relative merits of the M-series and the R6.
I have 3 x EOS M5's plus almost the whole range of EF-M lenses. I went that way when my injured knee could not hack the weight of walking any distance with a DSLR and lenses. I also have 2 x R6 units with the RF 24-105 f/4 and 100-500 lenses (+ battery grips). I avoided any of the M-series that did not have an integrated viewfinder, which left the M-5 and the M-50. As one who uses telephotos or just wants the stability I prefer a built-in viewfinder I tried the clip-on ones and rejected them as clumsy, bulky and fragile.
For me the M5, although earlier, was more of a still photographer's camera than the M50. First because of the extra control to manage EV compensation on the top of the M5 that was missing on the M50 and the M50 seemed to have been tweaked toward Vloggers, which it managed very successfully. To me, and looking at comparisons, the M5 was roughly equivalent to the EOS 80D with minor differences ending up about equal overall.
The R6 is a different beast. Eye Tracking and a super fast and efficient 20MP FF sensor, giving it an edge of about 1 stop EV over the R5, according to several technical reviews that I have seen - mostly because of the larger pixel size.
So, to me, the questions are: who would want one over the other and why?
1. Budget. The M-series is significantly cheaper, and so are the current lenses. Obviously the main body of RF glass is aimed at the higher end of the market as are the bodies. At one time I would have said any EOS 5D was going to be significantly better and more expensive than something with a 6D ID, but that has narrowed significantly as the main attributes IBIS, tracking and customization are all common to both the R5 and R6. So to me, the M and R ecosystems are aimed at two different markets, especially on price point.
I enclose some images taken on a hike at the Tongiriro National Park - formed around two active volcanoes in NZ's central North Island. All hand-held. For my purposes they did the job well, considering I was on a multi-day hike and wanted to keep the weight and bulk down.
Early Morning on the day I began my multi-day hike
Shooting into the sun to catch the mist rising from the valleys and around Mt Ngaruahoe volcanic cone
A close-up of a fungus in dim conditions
Just before dawn, the morning light silhouettes Mt Ngaruahoe with a crescent moon and Venus below.
2. Size: while the R-series bodies have reduced somewhat in size, the lenses are not that small, especially compared to the bodies and glass of the M-series. So again, different markets. The M series is great for travelers or hikers, or anyone who wants a very compact size MILC with not earth-shattering but acceptable lenses. I took 2 M5's hiking along with a lens on each and was very happy with the results. What is missing in the EF-M native lens line-up is something that approaches 300mm. Canon Rumors is suggesting that will be rectified this year, along with a potential M-7 that would be the equivalent of the EOS 90D but with IBIS, eye tracking, fully-articulated flip screen, and upgraded sensor and processor. If so that would likely keep a lot of M-series clients happy with their ecosystem and I would consider getting an M7 myself (and a EF-M 70-300 too). Time will tell. The M-50 is a great vloggers' camera, although the M50mkII was more hype than substance IMHO.
3. Compatibility: Both the M series and R series can access the vast legacy collection of EF and EF-S glass, but they do not have compatibility with each other, another thing that suggests there was no market overlap intended.
4. Input Output: Well a lot depends on the glass again. Both can work with the EF and EF-S lenses to make use of an enormous range of legacy gear. The improved sensor and processor of the R6 and its size mean that one can work in lower light and produce bigger prints than the older tech of the M-5. But if the mass of people are likely to work in more favourable conditions and willing to forego some performance for cost and size then the M-series would be great for tourists and travelers. The R6, while having lower MP count, has much uprated technology and could potentially provide better performance and larger prints, especially using the native RF lenses.
5. Ergonomics: The old question, 'what are you prepared to carry" becomes very apropos here... M5 bodies are small and so are the lenses, there are no battery grips, so it keeps things compact. The R6 is relatively small for a FF body, but the glass adds a lot of bulk and weight, and if you really want the performance you likely want a battery grip, so it bulks out a bit more.
In the end, I see the M-series as catering to those who favour serious compact size with reasonable performance at a lower price point, while the R6 is planting a stake in the ground for the new high-end Pro-sumer MILC market, where size and price are less of an issue, but performance and control are.
