Doesn't have to be in the OS. Enough to bundle it with the browsers. Same goes for all major frameworks as well, just ship jquery, angular, bootstrap and react

Doesn't have to be in the OS. Enough to bundle it with the browsers. Same goes for all major frameworks as well, just ship jquery, angular, bootstrap and react with the browser already, like a super long lived cache. If that's too steep for you, maybe a browser extension would be a good middle ground.