Having read the entire mailing list thread so far, the way this will be resolved is inevitable:
- Ubuntu is going to package Wayland in its main repository and support it. There's no way around it. In fact, see the quote below.
- Either the flavors will use Wayland as the system compositor and completely eschew Mir, or a Mir backend will be added to the version of Weston distributed by Ubuntu and the flavors will use a Wayland compositor running on top of Mir.
There's also some talk in the thread about working to get Mir support integrated into upstream KDE, but all of us who actually follow this situation know that's not going to happen as long as Mir is distro-specific, and there's no evidence that it will ever be anything else. The people suggesting that also doesn't address the problem that Kubuntu is only one flavor, and the Mir problem affects all of the flavors.
Also, there's this nice quote from Canonical employee Marc Deslauriers:
In any case, Kubuntu is quite unlikely to disappear or use a different distro as a base.Wayland will just work in Ubuntu.