VC4 works great in 64-bit, I've had WebGL running on some browser under Weston on ArchLinuxARM on a Pi3. I would expect V3D (VideoCore 5/6) to work out of the box on 64-bit too. Mesa very rarely introduces any unportable code – e.g. RadeonSI pretty much just works on FreeBSD/aarch64 :)
Wait - is the VC4/V3D driver open source? I feel like I missed that bit.
So basically, I should just cross compile RPi Linux and Mesa and it should work?
To be honest, I have been confused about the VideoCore driver situation from day 1, but I thought it was a blob.
(I am not sure Dolphin-emu would run with considerable performance, but damn if I’m not curious.)