64 bit raspberry pi os (no long rapsbian) is in Beta and Vulkan information is coming soon according to Eben Upton. Also there's an 8GB variant now but I don't think that's relevant to Dolphin other than the higher power delivery potentially allowing further overclocking.
https://www.raspberrypi.org/blog/8gb-ras...now-at-75/
https://www.raspberrypi.org/blog/8gb-ras...now-at-75/