It would probably do more harm than use. People would stop developing for FxOS because developing for Android would have a wider reach. Another reason is that,

It would probably do more harm than use. People would stop developing for FxOS because developing for Android would have a wider reach. Another reason is that, while I am not very familiar with internals, I think running FxOS app on Android is much easier than native Android on FxOS. Because FxOS app essentially is just a web app, which Android is capable of running out of the box. Can't say the same about Android apps. So not sure what's your argument for that?