Sorry, I could have been more clearer: discussionModel->updateUserDiscussionCount() makes a call to userModel->updateUserCache while commentModel->updateUser does not. Is that worth making a pull request?
Ah, so maybe more of a group account, where folks can do a "Post As..." option and change to the collective before posting, a la Facebook page management. That feature makes sense. Adding the retroactive switching to this plugin makes less sense.