Since nvidia drivers do not properly implement implicit sync, this protocol not existing is the root cause of flickering with nvidia graphics on Wayland. This MR being merged means that Wayland might finally be usable with nvidia graphics with the next driver release.
EDIT: Nvidia dev posted that support is planned in the 555 driver, with beta release planned for May 15: https://github.com/NVIDIA/egl-wayland/pull/104#issuecomment-2010292221
The Nvidia driver on Wayland has been decent for a couple of years and stabilized a lot over the past ~6 months. The flickering issue was specific to XWayland. Normal Wayland apps don’t have flickering problems (not quite sure why tbh), but XWayland apps would often rapidly flicker between 2 frames since it only supported implicit sync, which confused the Nvidia driver, which only supports explicit sync. Now with a Wayland protocol for explicit sync, XWayland can be updated to support it and resolve the flickering there.