Jolla Phone already had a Android emulation for Sailfish OS
There doesn't seem to be any free software effort in prong porting ART to a real linux system (which shouldn't be hard at all), which could've happened for years and I'm not sure (though shyly hopeful) the Librem 5 will change anything about that (so the only realistic option would be full emulation, which would require a good bit of power).
Edit: Just realized that you could theoretically run Android apps via Chrome. But shit, that'll be slow.
So far I know that there's an Ubuntu touch port of Anbox that works. It's a pretty good all-around solution considering the low container overhead and support for OpenGL ES 2.0