Should this be implemented, the cat and mouse game would likely continue.
The circumvention would be to for the server to some kind of proof of work of the “ad view” — use a service worker to check downloaded segments, and occasionally issue challenges that require sending a salted hash of the ad segments back to the server, along with a proof of elapsed time, without which the server simply refuses to serve the next video segment.
I can't see that actually working for YouTube in the end though. You can just download content and not play it, but in some background thread complete all the challenges.
You would need a way to prove audio/video on the end device/UA to the server and that's impossible AFAIK
The circumvention would be to for the server to some kind of proof of work of the “ad view” — use a service worker to check downloaded segments, and occasionally issue challenges that require sending a salted hash of the ad segments back to the server, along with a proof of elapsed time, without which the server simply refuses to serve the next video segment.