As kugiigi says, Ubuntu Touch is using an obsolete version of Mir (1.8) with dated Wayland support. Also, most of the Wayland support in Lomiri comes from Mir (the rest comes from Mir's support for "custom" Wayland extensions).
The consequence of that is that there's no much prospect of improving the Wayland support in Ubuntu Touch without first updating it to use the current version of Mir.
The good news is that is work currently going on to get Lomiri working with the current version (2.20) of Mir. As of today this works on the machines of the developers involved and is close to landing in both the Debian and Fedora archives.
However, it will still take significant time to get the rest of Ubuntu Touch migrated over to this newer stack. That is probably the task that can most benefit from help at present.
After all that is completed, it should be possible for Ubuntu Touch to track the current version of Mir, and Wayland support will follow Mir. It is also possible to contribute to Mir's Wayland support, but that won't help Ubuntu Touch at present.