In my experience, Waydroid works very well actually. The question is whether it wouldn't just be simpler and better to use AOSP (or Graphene) as the OS for these phones. In principle, a "Linux phone" sounds great, until you realize that there are close to zero Linux programs that are actually usable on a small touch display. The Android project already has done the hard work of adapting Linux to mobile devices and FOSS apps are plentiful and polished. The problem with the common variety of Android phones is control by Google, not the underlying tech.