I have seen multiple ideas based around the idea of not allowing lower levels access to higher leveled worlds, I dont like this concept alot. So I made up this other idea, guaranteed to satisfy everyone, atleast I think so.
Basicly, under the allow friend teleport switch in the options, there would be another button, which says: Require Teleport Confirmation, this can be set to on or off, and if friend teleport is not allowed, it will be grayed out.
The effect is whenever someone tryes to teleport to you with this on, there will pop up a window, sorta like this:
[Wizard Name], which is Level [Lv] wants to teleport to you. Do you accept or decline this? (Accept) (Decline)
Now, the character trying to teleport will get the message: Asking whether the target would like you to get teleported to them.
If accept is chosen, the teleporter will get the message: The teleport was accepted! This will also teleport that player to where they wanted.
If decline is chosen, the teleporter will get the message: The teleport was declined! This will leave them we're they were. They will also get a 60 second immunity against asking this person to have them teleported over there again.