Also, has anyone really done anything more than just tweak AOSP? Honest question, I don't know. If say Google completely abandoned the AOSP and went full Fuschia (I know this isn't likely), is there any individual or group out there that knows enough about AOSP to take it over?
Probably downstream vendors like Samsung have the technical capabilities. I seriously doubt that they'd be interested in continuing an open source project for wider use, but just maintaining their own fork would be totally doable.