You can change the information you put into the hash in my example to get them one go per site per day or one per year or even one per site ever. But without giving cross site linkablity that does you no good or giving google visibility into everyone all the time.

But that still doesn't get you to your desired unevadable bans, but with suitable parameters it can get as close as google's spyware approach while being much more private.

I think time a time oriented rate limit makes the most sense considering the limits in practice (attacker just gets access to another discarded phone, or tricks someone into authenticating for them via theirs)-- basically means the best you can do against dedicate attackers is rate limit them. So why subject honest users who may have good privacy reasons to use multiple accounts over time to worse effective limits than attackers?

But you don't have to agree with that to accept that schemes much more private than google's are possible.