The prices are getting scary now for top end Canon cameras. I mean, the R1 is likely to be £7k plus, if not £8k. Expensive for the hobbyist, that's decent
second hand car or very nice, b/new motorbike territory, just to put some context on it.
The R3 offers a lot but as I said in another thread, I wouldn't drop near £6k on one, especially as already owning a 5Div, the difference between the 2 just isn't enough.
I may be tempted into the R system though if the much rumoured crop R is ever released, it's likely to be a 3rd of the price of the R3 and offer much the same at a guess, with slight knocks from the cripple hammer, say 20fps instead of 30 for example.
That said, when the times does come to replace my 5D, if I'm still alive by then, then I'd go mirrorless, as it is, like it or not, the future.