Plan is to update mesa post-sync this week. We already have the
nvidia-beta-driver-current which is at 515.43.04 for those that need it. The reason
nvidia-glx-driver-current is still on the 470 series is because once again nvidia decided to drop support for some cards.
As is, if its updated users with cards that were dropped will just boot to a blank screen and would need to manually switch themselves to the 390 series driver before updating to avoid this. Which means they'll also lose a lot of improvements that have occurred since 390. The maintainer @Staudey wanted to avoid this and held back updating it to hopefully find a better solution, reality is there is not one. Nvidia have done this many times before and will do it again.
Kernel is unlikely to move off 5.15.x next week as it is being evaluated as a future LTS kernel for Solus.
No, Solus does not update drivers because proton experimental decides to update its requirements.