It seems like the G-Sync/Freesync support under wayland has arrived in driver 525.53, I can see the option on KDE Plasma now!
EDIT: However while the option is there, gsync itself doesn’t seem to kick in, I do believe it could be due to this specific part nvidia driver part how kwin is designed, bug → 450914 – Wayland, games on Nvidia are force vsynced