The reddit AMP pages you land on from Google searches are particularly irritating. You aren’t logged in when you go to them, and various UI expectations are broken. Web packaging could help here since it would remove the google url, allowing cookies/sessions to function again.

Web Packaging (at least on its own) wouldn't help with that, since the whole point of that standard is to allow content to be prefetched from a CDN (like AMP pages currently are), and CDNs can't cache content that's user-specific.

What _would_ work is serving the main content immediately, then using JS to fetch user-specific stuff after the page load.

... and we’re back to optimizing for fast delivery of the page that loads your page.

Right, which you can’t do now, but could do after the main page url is yours again.

I meant from the other direction. Like Reddit could pull the AMP versions of pages users link to.

As for their implementation of AMP pages for Google's use, I think that's sound strategy. People landing on Reddit from Google are at the lowest level of engagement and a lot of sites serve more ads conditionally based on your level of engagement. Native visitors get a better experience, logged in contributors get the white glove treatment.

CloudFlare, Bing, Baidu, and Yahoo Japan run their own AMP caches. I agree that it makes sense for external link heavy sites like search engines and Reddit.