No other site has gotten away with this. The last time I can recall someone attempting something similar was Digg (remember them?) with the "Digg bar" which added a toolbar linking back to Digg for all of the internet, and well, what happened to them?
Now, I'm visiting https://news.google.com/news/amp?caurl=htt%3A%2F%2Fwww.nbcne.... in order to get content from NBC News, while http://www.nbcnews.com works just fine. The writers of the article I'm reading are (ostensibly) hired by NBC news, not news.google.com, and there's no way to get to the same article on www.nbcnews.com unless I do something really awkward, like go back to Google and hunt and peck (I'm on my mobile phone, remember?) to type in "site:www.nbcnews.com article name".
I have hate for the UI of AMP itself (they broke scrolling down to get to the URL bar somehow), but that's also a distraction from the fundamental contract that AMP breaks.
Google would (rightly) get pissed if I made my own search page which "rebranded" Google search results to have my advertisement and then present the Google search results as coming from me; I hate them for doing the same thing to news publishers.