Feature proposal: single user instance

Joomla User Plugin enhancement: Ability to avoid simultaneous logins.

Deny simultaneous logins: If a user wants to login and another person is logged in with the same user, the plugin denies the login and throws an error.

Force unique user session: If a user wants to login and another person is logged in with the same user, the plugin can logout the existing user.

Currently it's not possible to redirect or display a message for a specific user, but i think it's a general feature which could be implemented and used in different situations like the abilty to logout a frontend user from backend. So, any ideas ?