[zozbot234]

> ...Even Mozilla wasn't able to pull it off

Mozilla did not try a purist approach. Their Boot2Gecko was built on AOSP downstream kernels and proprietary drivers. (Then again, there was no such thing as a truly 'purist' device back then, even in non-AOSP land. So they just did what could work at the time.) If you want to explore that kind of approach, there's things like UBPorts and Droidian. They might even make sense, if they end up being able to function as AOSP-compatible Generic System Images (GSI's) and run on mostly any Project Treble-capable device. Make no mistake though, that's a lot harder than doing everything properly in upstream and restricting one's attention to hardware that's compatible with that approach. If only because you're not forced to keep up with churn in the AOSP-native interfaces.