My 2 cents
It killed any desire i had to stick with Canon at this point.. Right now im running a Sony A7 III with the 55 f/1.8 Sonnar and 90mm f/2.8 Macro in addition to my Canon 7D Mark II, 15-85, 70-200 f/2.8L IS, Sigmalux and 100L..and a 150-600 Contemporary that is shared between the two
The R didnt make me want to sell my Sony off and add the R in, it made me want to do the opposite (and i likely will be doing so shortly)
Reasons?
-No joystick
-Big heavy expensive lenses and heavy reliance on adapting, i almost bought the 50mm f/1.4 for my A7III because i got an amazing deal on it.. but the size and weight just was not suitable for my needs, the 50mm f/1.2 is even larger. Lack of a concrete lens roadmap is also harmful from my perspective, the "rumors" ive heard is that basically we're going to be seeing big large f/2.8 zooms for the upcoming future
-Needing to adapt EVERYTHING pretty much
-Poor speed when using tracking AF (3-5fps when you enable tracking AF, i get 8 with live view or i can fire off a 10fps burst without, Either is significantly better for my types of shooting)
-No in body stabilizer
-Single card slot
-6D-like ergonomics
-The thumb touchpad thing one reviewer noted some problems with it registering, i know my fingers and such have issues with such things and i know it would quickly be an annoyance for me
Im not hating on it entirely, i do think its a lovely looking camera, and the lenses are cool, but its just not the right camera for my needs. For my needs im simply better off trading off my Canon gear and investing in my Sony at this point (Basically, getting the lovely new 24mm f/1.4 GM, 24-105 f/4 and the 70-200 f/2.8 GM which will complete my system) which is a shame really, one or two tweaks to the R would have me doing the opposite... I do like the 35mm f/1.8 Macro for example, quite a lot in fact. But thats just not enough and not worth it.