I don't see why it wouldn't be possible -- you can use `git log` with a formatting rule (like `--pretty=email`), and then parse the `From:` fields and group them by domain.
The rest is application specific: you'll need to determine whether you want to/should normalize subdomains to their parent, for example.
Yeah, `git log --format=%ae | sed s/.*@//` will get you most of the way there, and then it’s down to how you want to deal with the domains themselves, as you say!