More than once now, I've signed up for a PL that sat full but idle because the PL creator didn't realize that the PL does not start automatically once enough teams have accepted the invititations.
Assuming there's good reasons for doing things that way (I can see some arguments for it... but that's not the point of this post), I think it would be a good idea for a BB-mail to the PL creator to be triggered when an accepted invitation fills the last slot.