I think it's funny how people get hung up on MP. More MP does not make a camera superior. It's nice in some situations to have super-high resolution but as a demanding Wildlife photographer I have to say that sometimes 45 is too much. Pixel density can become a problem with fast moving subjects. If I'm in Alaska shooting a fishing bear or a perched Eagle then yes, 45mp is great. If I'm trying to shoot something that moves fast I have to bump my shutter speeds (and ISO) way higher than I ever did on my 1 Series cameras to get a sharp photo.
I'm excited for the R3 at 30(some) megapixels. I won't have to fight with pixel density and the LP-19 battery is going to drive my 600f4 II faster getting me better target acquisition. This has always been a problem with LP-6 based cameras from the 7D on. Battery life will also be better than a gripped R5 from my experience with those batteries. So for $6000 you're going to be getting much better tech that is designed for fast action. Maybe less resolution, but with better tracking and acquisition, probably better EVF, faster readout speeds, a truly sealed body, etc.. . Remember that the 1DX only had 18mp (and the 1DX II/III only 20) and cost more than this camera and you certainly didn't see it replaced on sidelines with 5DIVs. As far as the A1, from what I'm reading you can get 30fps at 51mp, but only in very limited conditions.
I'll be keeping my gripped R5 for slow stuff, but the R3 will likely become my action camera.
I am hobbyist who spent way too much on gear to play with. I don't see myself in the long run owning this many bodies and 3 systems of glass. I would rather have 1 body that can do everything I wanted. Cropping helps me a lot for some of the other stuff I do outside of wildlife. I will buy the R3 and play around with it, that I already know, but I think the price point if it was 6k is too much. That would make the R1 flagship into 8k territory. I get that the 1dx miii was 20 mp and cost more as a flagship. We will all see soon enough what Canon has, but I am just hoping its not the 6k price tag as it is rumored to be. As for the A1 the biggest limitation to the 30 fps is probably the requirement is Sony branded glass (which some need serious refreshes) ., the compressed raw etc all that doesn't bother me much. For someone with no real brand loyalty, you can see that I am weighing results( or specs) vs price points. I would not choose body with less functionality for a similar to price point to a more functional body. The a1 really is a great body (grip is needed for sure) but Sony's glass doesn't compete imo. If I could slap my RF glass onto a sony body that would be great lol.