Samsung's been working on deX for a long while now, so you'd have to convince them to give up all of their desktop related work.
I think maybe you're referring to Samsung Dex, for which, as you mention, Samsung has invested heavily in their own desktop.
But I'm referring to Samsung's Linux on DeX project, which runs a modified version of Ubuntu (developed by Canonical) in a container, and already has a Unity-like desktop, which if I'm not mistaken, is based on MATE. Also, Samsung Linux on DeX allows installing at least a few other distros and DEs.
You also have to get Mir & Unity8 working on android, which would in itself be a huge task.
Yep, 100% agreed. I'm under the impression that the above mentioned Unity-like desktop (because it's based on MATE) doesn't support Wayland, and so can't (yet) rely on Mir as a compositor. Whether Linux on DeX is currently capable of using a DE that supports Wayland, I don't know. But I imagine that if it's not yet possible, Samsung is working on it.