"I can't say I'll miss Unity."
Neither will I. It was designed on exactly the same desktop-to-mobile premise as the Windows 8 interface and misguided for the same reason - different use cases need different interfaces.
What I will miss is the effort to get a non-spying OS on a non-overpriced phone. One possible outcome might be that commercial investors restart the Ubuntu phone development going without the overhead of pretending that the same interface can work on a desktop with the downside that they'll insist on cloning the Google/Android business model.
"Linux on the desktop has always been marginal; it's really a server OS that works okay in embedded applications too, which is why Android could use it."
Think this through. Why can what you allege to be "really a server OS" work okay in embedded?
It's because any OS modelled on Unix is a portable and properly layered system. Portable means that any part of it can be compiled for different CPU architectures. Layered means that the kernel can carry a run-time appropriate to the use case: a cut down payload for embedded, a mobile-oriented* payload for Android or a standard set of Unix utilities with or without a choice of graphical interfaces for desktop or server.
No it's not "really a server OS". It's an OS. Just because you struggle with it doesn't mean that our elderly relatives can't manage it when we use it to rejuvenate their old PCs.
*The modular driver system helps here.