This is actually the trajectory of both Apple News and iAd before it, which is what started out providing the ad service for Apple News. Apple would like to do a high quality solution, and then keeps relaxing their standards when there's not enough buy-in from the content providers. They were forced to allow the non-curated news formats to have sufficient content.
It'd be a big one-time lift; and of course there'd be annoying constant breakage to fix as sites update; but News.app could always fall back to rendering the original article URL if the News backend service's currently-deployed parser-transformer for a given site failed on the given article. It's make things no worse and often better than they are today.
In this specific example there is a very big difference between producing a format for use in a first-party app vs trying to replace standards for content used across the web.
I mean... sure it could have? There could have been an independent "AMP Foundation" that forked the standard away from Google and owned the evolution of it from then on. Like how SPDY was forked away from Google ownership into HTTP2.
https://developer.apple.com/documentation/applenewsformat
The problem is that people don't use it. I imagine it's a chicken/egg thing, the audience on News isn't big so it isn't worth the publishers time catering to an entirely new format, the News experience is crappy so the audience doesn't grow.
They could have insisted that everyone use their format but I suspect publishers would just refuse. It's not exactly in a publishers interest to help boost a middleman between their content and readers.
I'd be really interested to see what Apple's approach would be if they used more web technologies (since that's what publishers are using today anyway). Even just a webview with disabled JavaScript would get a ton of the way there in terms of performance. They have WebKit engineers in house that could probably tweak it even further.