The Mutter 3.19.90 release adds basic startup notification support on Wayland. There is also now pointer motion, locks, and confinement support on Wayland.
Details on the other GNOME Mutter 3.20 beta changes can be found via the news entry. GNOME Shell 3.19.90 meanwhile correctly identifies VPN secret requests, adds an audio device selection dialog, and has various other changes.
GNOME 3.20 will be officially released in about one month from now.