So you don't need to invalidate the auth tokens. You just need to be able to delete a session from the cache to do revocation on long sessions. And this works with just backend changes, no client hockey-pokey needed.
Nope. Let's say you have a rest endpoint that accepts a Pokemon id to add to your collection. If you cryptographically sign a cookie that says "I am this user id" you can assume the request to add the Pokemon to your collection is valid. There's other business logic to perform, sure, but "I am this user" is taken care of for you.
What Google is proposing is the ability to save a long-term cookie that says "I am this user" and a short-term cookie that says "I'm signed in". The requests periodically say "am I still signed in/am I still this user" and the server can periodically (eg not every request) look that up in cache/database.
This just moves the problem a bit - if you want to log out a user, you can just erase the cookie key from the server side; the cookie will be just random noise at that point.
This approach, of course, assumes that your keys are user specific, possibly generated from the password.