I would settle for something that simply turns the screen black and turns audio off whenever ads play. I don't care if YouTube gets paid for it, I just want to decrease the value of ads and prevent myself from seeing them.
If the ad is just blacked over, it is still loaded, and they wouldn’t know.
If it became a common thing, they'd have to add detection for it. Not necessarily to stop people doing it, but to ensure advertisers aren't charged for invalid impressions. Practically every major ad network has adblocking detection; they just don't always make it obvious (e.g. they might silently log it).
Well they also infest the client side since they likely developed the main part of your web browser, so they can still know there's a black cover in the DOM.