I love this. And Europe can make these tags mandatory for all ads and trackers.
I'd expect the push to come from browser vendors. Either by blocking ads that aren't in those elements by default, or feeding them garbage data.
"user-visible text or image(s) meant to advertise a product or service, separate from the primary purpose or offer of the page in which it is embedded"
... or something. IANAL.
This won't really hit people doing self-serve or custom ads much, but it'll cover the vast majority of the web.