Ok so this is a noob question but is there any reason why we can't have an AV Receiver running Android TV. I feel like that would be awesome because we could have some really powerful hardware(AV receivers tend to be quite large so hopefully room for powerful SOC with an almost desktop grade Heat Sink. Maybe I am misinformed about the reality or this ever existing but this would be perfect for me and would allow me to have one box under my TV instead of multiple.
You could but that would be a similarly problematic idea like the TVs with AndroidTV embedded. You'd have to replace the whole 500$ receiver if it stops being supported (or it isn't updated, or it has a crappy hardware) instead of a cheap 100$ Nexus Player box. AV receivers and TVs easily outlive all the media players and STBs connected to them.