G[enerative]EO is already a thing, there's no way they'll just let all that value be extracted for free.

You'll pay extra for those. The ones marked as adds will be cheap. Like how the expensive placement is into the movie (e.g. Apple) rather than the disruptions of the movie.

they'd have to be incompetent not to put stealth ads in chat. They could make so much money with stealth ads in chat.