> Notably, some instances of back button hijacking may originate from the site's included libraries or advertising platform. We encourage site owners to thoroughly review their technical implementation...

Hah. In my time working with marketing teams this is highly unlikely to happen. They're allergic to code and they far outnumber everyone else in this space. Their best practices become the standard for everyone else that's uninitiated.

What they will probably do is change that vanity URL showing up on the SERP to point to a landing page that meets the requirements (only if the referer is google). This page will have the link the user wants. It will be dressed up to be as irresistible as possible. This will become the new best practice in the docs for all SEO-related tools. Hell, even google themselves might eventually put that in their docs.

In other words, the user must now click twice to find the page with the back button hijacking. Even sweeter is that the unfettered back button wouldn't have left their domain anyway.

This just sounds like another layer of yet more frustration. Contrary to popular belief, the user will put up with a lot of additional friction if they think they're going somewhere good. This is just an extra click. Most users probably won't even notice the change. If anything there will be propaganda aimed at aspiring web devs and power users telling them to get mad at google for "requiring" landing pages getting in the way of the content (like what happened to amp pages).