I have seen a similar request, not quite the same though and it has no reply so heres another stab at it :)
Would it be possible to have a expire date available when creating a user so that a nightly chron could auto remove the users when their time had come?
Right now it's not possible.
I welcome patches, but development has stalled as I have no time right now.
It would need a database schema change (adding an expire date) and the management of it.
Or maybe better add a "user_options° table and create the hooks for plugins to add features and functionality to user management. (i.e. password expire also comes to mind, but could also be used to have additional fields for registration and so on)
This would need more work though.