Pretty sure it would still be links behind the scenes. The argument is only for user-facing links to „get simpler“ on the basis of links with tokens and whatnot being to complex and easy to get phished with. Don‘t forget, in Googles vision everyday users won‘t interact with keyboard/mouse or similar in the not too distant future. It‘s all Assistant and device-agnostic ambient computing.
Portal is moreso an alternative to iframes than an alternative to links. But it's true that it could very well make it more likely for a portal to another site to be included in a page rather than using a link.
That's why it's so strange. There isn't an alternative that isn't just a link with a different syntax, so why bother upending the internet for it? Things have worked pretty well for decades now, the whole point of writing a protocol is for long term usage in a changing world. So far so good!
It a bug that's breaking some JavaScript that renders the AMP page header. It's breaking a link Google is supposed to generate via their mandatory included js for AMP pages.
I though links was a pretty important part of HTML, and so people took care to ensure they work?