Does this mean I could finally enjoy HDR content on my OLED HDR monitor?
You can right now. If you are using KDE, it should work with mpv, though you might need to launch it from terminal with a few flags to tell mpv to use HDR.
If you’re not using KDE, you can launch gamescope with the hdr flag in the tty and have it launch mpv.
Though I’m not sure any browsers have working HDR. I think Chromium may have some stuff in progress. Gnome Web may get it since WebKit supports HDR and HDR is being worked on for GTK.
gnome iirc also has merged the wip protocol so it should work on gnome too