You ask an excellent question. Especially for an amateur like me.Fair enough. To be accurate, I should have said people who are happy with what they have already, even with the availability of an R5 at whatever price Canon is charging for it.
If I would only shoot stills, I think I would not look at a new body.
I bought the Canon 60D with the idea of using it in still and video. This is an excellent body.
It has some limits in low light and this was a bit of a problem for me as I shoot some conferences for my job and also some low light photos in general.
I love this special feeling given by light just before sunset, called in French "between dogs and wolves".
However, it had been a step change versus my Canon 350D, mostly used for astronomy pictures.
I also love art and normally I am visiting 80% of the key exhibitions in Paris, France.
Indeed, some exhibitions are simply fantastic and gather master pieces I might only see once in my life. So I like to have a picture of it.
What I do is that I take the pictures of the full exhibition when authorized. Again low light is the problem with exhibitions.
When the 6D was at the end of its official sales life, the price was divided by 2 and I bought it.
I really enjoy its capacity in low light.
What remained a frustation on my side is the lack of high resolution quality in video.
The stills with both bodies are fantastic but the video quality not that great at all in comparison with a Lumix GH5 or GH4.
I also have a Canon XA30 which I thought would produce better video quality but it is not really the case.
Canon XA30 is a perfect video camera for interviews, conferences and documentaries where you do not have time. Easy to use, lots of automatic help.
But when you have time, you put a tripod on a seaside for the world championship of windsurf, you are dreaming of fabulous high resolution videos and NO they are just ok. The video quality is not detailled oriented and this is annoying. Contrary to Lumix GH5 (again).
So I bought in 2018 during Black Friday the Lumix FZ1000 where I get this high resolution video camera, but it is a bridge and all my L lenses can not be used... However, video quality is impressive. FZ1000 is kind of a small GH4 with IBIS !
So Canon R5 might be the body I am hopping to find: excellent stills but also excellent videos quality.
Where my Canon lenses could be used...
If the video quality is not there, I will not buy it. I will continue with my current bodies.
Attached: exhibition on the French art during François 1st (16th century) Body 6D
Brand new streets and shops in my district: Body 6D
I hope it clarifies why people like me are interested in such a body.