I’m not sure what you’re referring to by “this”, so I’ll try to answer all possibilities. Yes, hardware accelerated video playback is available equally in Wayland and Xorg sessions. The high CPU fix mentioned above in theory applies to both, but in practice seems to be most significant in Wayland, because Wayland apparently lacks 2D blitting acceleration that Xorg has. And the lack of window decorations is indeed a Wayland-only problem.
I’m personally hopeful Wayland moves toward allowing the shell/WM to add-on the window decorations, as is the case for Xorg. But the bare mpv window in Wayland actually isn’t too bad. You can still move it with a mouse drag, and resize it with Action+middle-mouse-button (where Action is Super by default but is also configurable in gnome-tweak-tool).
P.S. You can quit mpv using the Q key at least (https://bugs.launchpad.net/ubuntu/+source/mpv/+bug/1720835).