Can someone confirm this part of it? I'm highly, highly dubious that these TVs are sending back random ambient conversation -- for one thing, it would be a truly monstrously-huge stream of data, no?

I certainly believe that it sends back data when you use voice commands, ofc (both for advertising and product improvement). But this would be the first real case of something that's been a 100% false conspiracy theory for over a decade, which feels... unlikely. Kinda like someone finding a Sasquatch.