They post says Jeff Hostetler, the author of the patches, will make a blog post delving into it. So it's worth bookmarking that post and swinging back. It's bound to be an interesting one!
Apparently git 2.16 had a fsmonitor hook for external filewatcher like watchman (it got passed me): https://github.com/git/git/commit/def4376711f607914bfb784f8d...
This kind of change needs to be tailored to the platform, it says just Mac (FSEvents?) and Windows (ReadDirectoryChangesW?) for now. So can we expect Linux (inotify?) and BSD (kqueue*) in the future?
Anyway, I hope this venture is fruitful. The premise of having cross-platform file watching without needing an extra application is delightful.
Thank you Jeff!
* I believe one area that may be tricky is kqueue, I believe it has limits in watching directories, needing a file descriptor for each file.
P.S. I would like to drop a link to entr(1), a lightweight cross platform file watcher: https://eradman.com/entrproject/