The reason this is an issue is that the sub value changes often enough that intergrations ignore it rather than bother users with having to re-OAuth.
As far as what Google is doing in the bug bounty, that's a good question -- we don't know. The author is proposing two new values, for the domain and user, that wouldn't change in the cases that sub changes now, but would change in this case.
As far as what Google is doing in the bug bounty, that's a good question -- we don't know. The author is proposing two new values, for the domain and user, that wouldn't change in the cases that sub changes now, but would change in this case.