So just to put a bow on this post, I pre-ordered one of these. Since I hesitated until Saturday, I will almost assuredly not be seeing mine for a while. I have a 5DSr, and shoot almost exclusively scenic, although I am starting to branch out into some more wildlife. I also like to shoot nightscape stuff. Here are my final thoughts, after all the initial info/hype/criticism/etc.
1) I have heard all the hand wringing about overheating. I as of now do not shoot video. I could not even tell you what the supported video modes are in my 5DSr. I may play with video some on the R5, but cannot imagine I will use it much if at all. The only interesting thing immediately would be screen grabs of 8K footage to make 33 MB images from. But when one looks at all that would be entailed to accomplish that, the 20 fps or 12 fps modes are likely much better. So I could care less about video overheating.
2) I wanted to leave MFA behind, and get the advantages of reliable AF. The R5 appears to satisfy that and then some, with what appears to be a fantastically upgraded AF system over my 5DSR. Just having 100% coverage for AF points alone make this a winner for me, not even considering how much more capable the AF system is.
3) I wanted to have better hand-hold-ability for images, as I am frequently in situations where a tripod is just not an option. The IBIS combined with IS looks to totally accomplish that.
4) if I want to shoot wildlife, the new animal AF and frame rates look to make this a killer rig for that.
5) Better DR and high ISO than the 5DSr mean this should be big jump up for low light or nightscape over the 5DSr.
6) Even considering the change back to an AA filter, I am almost certain in real life the delta between the 5DSr and the R5 with respect to resolution will not be discernible in any practical scenario, including printing at 20 x 30 or larger. I will keep the 5DSr for the short term anyway (it is already worth almost nothing as a used camera) so I can do my own testing on this, but I doubt I am really losing any practical landscape shooting capability by swapping to a 45MP body from my 50MP body.
7) Other than the expense, the swap to RF lenses looks very attractive. My current kit of EF 16-35 f/4 L, EF 24-105 f/4 L Mk I, and EF 70-300 f4-5.6 L have been great. But moving to the RF 15-35 f/2.8 L, and the RF 24-105 f/4 L right away, and then eventually maybe the RF 100-500 f/4-7.1 L (with maybe also the RF 70-200 f/4 L if it gets released and looks compact) will be a definite upgrade.
Lots of other compelling features for me, but those are the top ones. I have been saving up money over the past 2.5 years to make the jump to Canon mirrorless once they had a compelling offering. And I have always said I love my 5DSr, but the things I have wished could be improved were 'no more MFA worries,' better AF, faster FPS, and better high ISO and/or DR. The R5 gives me all of those things. I imagine a high rez R body in the 60 to 80 MP range will be a good camera, but in practice the delta in resolution is not that great over 45MP, and unless it is 2 years in the future at least, I expect it will not match the R5 on FPS, noise, or DR.
So this becomes a rather nice retirement present for me, once I get myself retired (hopefully no later than September, we will see how that goes...)
ML