I think it's good and bad.
Good - When the attacking driver is in a genuine position to overtake then no foul play can come about.
Bad - When the attacking driver is not in a genuine position to overtake, then the defender driver should be able to take the line back up, otherwise he may as well just pull over and let him pass.
There are examples of good and bad with the Schu vs Ham battle at Italy.
I think it should be: You can only change line once and ONLY resume your line if the attacking driver is not in a position to overtake.
I mean like 2 cars going onto the straight and the car in front thinks he's got a run on me and makes his first and only move, only to realize that when they get near the braking zone that the guy behind it no where near as close as he thought.
I suppose drivers could abuse that as well ?