GitHub already allows you to follow other users publicly. It displays your followers publicly, too.
Wouldn’t it be possible to make your GitHub account even more sociable? Someone could build a third-party application for this. Here’s the sequence of events I’m imagining to make GitHub-as-a-social-messaging-platform (SocialHub?) possible.
You authorize the app to make a public repo under your account. Everyone using SocialHub has a repo with the same name. Only that respective user has write access to it.
When a user makes a post with SocialHub, he or she is actually making a commit to his/her special common repo. The post can be the message, and/or the message can be written into the file of the repo. That way, a message history is preserved within the commits to the common repo.
When other users interact with someone’s SocialHub post (commit), they are actually just using the GitHub comment form/API call on that commit. The same commit that was made to the common repo.
With this structure, pulling up a SocialHub user’s post history is as simple as looking at the commit history to his/her public, common repo. You could make it even more interesting and make the common repo contain a lone markdown file, containing only the most recent post/message. A history of interactions to other users is available simply by listing the comments on each commit.
You could build this app, I believe, solely as a front-end implementation using GitHub’s available API endpoints. No database required.
Private messages could be passed via a common private repo on a user’s profile. He or she would have to grant access to other users before they could comment/view his/her “private” commits/posts.
Wouldn’t this be a pretty cool social messaging service? It would be completely intertwined with your public GitHub code commits and could leverage the expanse of git and GitHub.