If you want to learn more about this, read up on 'continuous deployment'. I remember when I was first exposed to it it seemed dangerous/scary but with the right culture changes it can work really well; lots of companies do it.
It's not as ridiculous as it sounds as long as the testing and verification happens as part of the PR.
Sure, but then you are just begging the question: if you have a better process for release verification you might not be need any per-commit code review at all.
iirc Google does it, it's not ridiculous at all. You need a lot of automated tests and canary deployment to pull it off though.
Not really. Googler merges to HEAD, but systems aren't running directly from head.