"UIs are important."
Quite. The best approach seems to be that undocked you have a phone interface, docked you have a desktop interface. One of the things about Unix-based systems is that the UI is an additional layer on top of most of the rest of the system and the interface between the layers is clean enough to swap UIs as needed. Of course if you then try to run an application that needs the desktop interface when undocked you're in a hole of your own digging.
Having said that Ubuntu decided that what they really needed was an app-centric interface on the desktop to prepare the way for use on the phone and got it out even ahead of W8. I don't think it's proved as popular as the more traditional desktops.