As to who the M line was targeted for, many pros bought into the M line for personal use, web vlogging, etc. Again that matters little, there was and still is a very active M following and canon has multiple versions as they enhanced and improved the line. It isn’t like canon didn’t know what they were doing when they did the R and RP, they had a decade of experience already.
As to live view, it doesn’t matter how people had to hold the camera to use it, that doesn’t negate my comment that the low light issue causing grief in a sensor-to-lcd (or evf) had existed years in the DSLR line. So this isn’t a “kink” of mirrorless that has to be worked out.
Finally, there isn’t any other DSLR model than the 5d4 to move to that is better than the 6D, assuming IQ is paramount which is usually one of the primary reasons one looks to upgrade along with a host of other features you gain. Of course you may want to bring in the 1dx2/3. Even then from just an IQ perspective, it might be a wash, maybe the op is open to a 1D series?
Therefore yes the 5D4 is a worthy upgrade, if for no other reason that there’s not too much else to choose from regarding IQ. Ignore that it has more resolution, has more features, is built better, has dual slots, AF is better, and for many has better ergonomics. It is clearly one of the fan favorites in the canon DSLR space. If the OP is for a mirrorless option, then the R is the closest to the 5D4 for resolution and function, with a gen 1 eye AF system thrown in. I think it goes for about the same, maybe less. However I would like to some indication of the OP considering it, and at this point, it appears not.
I have all three, an M series, a 5D4, and an R6. I feel I am qualified to talk to these points simply due to experience and ownership. And I had an R and 6D. So I don’t have to live vicariously through others’ accords, or theory, and I don’t have some sort of emotional attachment to just one type of canon product, ie I can be objective.
Wilt, I remember back in the day on how you stated the 7D2 couldn't do what was touted of it for low light focusing. So you would theorize a bunch on it in your posts or used others' posts as backing. Then you bought one and was surprised that it could in tests you performed in your attic, if memory serves me correctly. If you haven't bought any mirrorless, it might be time for you to consider an "upgrade".
Maybe you have already, and I don't know it, but to experience it in the M and R line up, it will make you appreciate certain things and really wish for others.





