> What I know I care a lot about is when a tab I haven't looked at in three days is suddenly using CPU time _at all_. Just make it so background tabs get severely limited in their ability to do background execution and eventually get stopped entirely, and the problem is essentially solved.
Chrome does throttle background tabs: https://developers.google.com/web/updates/2017/03/background...
It doesn't throttle them all the way to zero, though. If they did that they'd break things like sites that change their favicon to signal "unread message".
(Disclosure: I work at Google, though not on Chrome)