They’re already here. I even pay Hulu extra for no ads only to be greeted occasionally by a statement that due to licensing agreements a video has to have ads. And even the things that “don’t have ads” have ads for their other streaming videos, or try to cram ads in between auto plays.
Case in point: I expect ads to arrive (within a decade) to streaming videos, much like they did for cable.
(Cable's main advantage in the early days was the lack of ads - or so I'm led to believe)