The project to port MATE to Wayland using Mir has made some progress. Mir support for the Layer Shell Wayland protocol has been improved and merged into master. Wayland support for MATE Panel using Layer Shell has been merged as well. There’s still a long way to go before we have a fully usable MATE-on-Wayland session (most of the MATE apps don’t yet support Wayland) but progress is being made.
Meanwhile, I’ve also fixed a problem specific to the mate-wayland snap. It had an issue where GTK3 apps would crash as soon as they were launched. I fixed this by writing snap-out, which cleans the environment of launched applications of snap variables. Full explanation here.