In theory, the Android runtime environment could be ported to most desktop environments. I have seen Dalvik running on Windows 7. I used to be CTO at a company that developed an Android runtime for WebOS. You might infer they could do the same for similar platforms. Jolla has demonstrated Myriad's similar technology running Android apps in Sailfish. So while there isn't as cleanly defined boundary between app runtime and OS as with JavaFX, which is designed to be cross-platform, in practice it is possible to move the Android runtime across platforms with good results. It should even be possible to put Android apps into realizable windows in desktop environments.
There is a lot to be said for taking an environment with a big following and making it cross-platform vs making a cross-platform environment and hoping for adoption.