> Didn't we just add MultiLoopChildWatcher in 3.8?

Yep, that's correct: https://docs.python.org/3/library/asyncio-policy.html#asyncio.MultiLoopChildWatcher

I wasn't aware of that, but it would explain the current lack of usage. I'm generally in favor of Andrew's idea to deprecate the watchers subsystem, but perhaps if we go through with that we should remove MultiLoopChildWatcher from 3.8 (if it's not too late to do so) instead of deprecating it.