Check-in and check-out functionality with real-time reporting

[joleys]

Would it be possible to add functionality to 'check-out' an attendee as soon as he/she leaves the event? This closely resembles the 'cancel' functionality, but should also add a database entry with the timestamp of the check-out.
Besides it would be nice to have some realtime reporting with the active attendees, including check-in time, duration of attendance, average duration of attendance,...