Video streaming is too slow to adapt, but I see a way for advertisers to check if you watched an ad even if you didn't interact. Specially if the site already uses the webcam.

That was the thought that immediately came to mind when I saw this article --- as if unskippable ads were bad enough, with this they'll be able to make ads that you can't not watch, and the whole thing just disturbs me greatly. No doubt it'll get spun into an ostensibly "user-friendly" "automatically pauses the video if you look away" "feature"... but the motives are clear enough.

Cue black mirror episode: https://en.wikipedia.org/wiki/Fifteen_Million_Merits

If I close one eye on this it still finds center of the closed eye where pupil should be.

Presumably you could close both eyes but I can't test that for obvious reasons.

So this specific implementation might not work for that.

That is a pretty cool idea but I can't see it being fast enough to dynamically update the video stream could it? Very cool idea though.