We're still talking about an environment that can execute practically any code. I'm sure the next thing advertisers will do is download 100 static images and animate them with scripts.
I mean, advertisers have been using GIFs since the early days of the web. The benefit here is that audio won't autoplay unexpectedly, which nobody ever wanted ever.
Alternately they've overlay a transparent play button over the entire pay so the moment you click it counts as a "user action" and the video plays. Seen it happen on a few sites. They combine it with something like forbes uses with a "quote of the day" interstitial.
Or an opaque overlay with ' click here to read article' that also triggers the video
The main point of the feature is to prevent sound. A muted video will pass the test.
"…users now have the ability to turn off all forms of auto-play, including silent videos." (Emphasis added.)
The article later clarifies: A video with a silent audio track will be blocked from autoplay. A video without an audio track or a muted video will not be blocked.