Just a plugin concept …
Add a form with a button to each user profile, post or wherever you want it named Follow orUnfollow. Show the button only if
is_user_logged_in(). You may use a widget for the form.On form submit update a user meta named
followsfor the user who clicked the button and another one namedfollowersfor … well … the user who just got a new follower. Use the user IDs as a serialized array (yes, ugly, I know).Create a dashboard widget or a whole page where the access is restricted to users who can follow or be followed. Query for the user meta
followsto get a list of all authors the current user has subscribed to and then query for the posts from these users.Get the user meta
followersand print a nice list of her followers.