This is actually a very good idea and will put an end to players trying to charge too early or edging forward. So many times you see the players blatantly not 10 yards back and for the ref it isn't always easy to spot as all the players usually come forward the same distance.
Problem is when they go back to their positions the wall edges forward again.
If the paint really does disappear quickly then I don't see a problem with it. Most ref's pull the wall back to the required distance anyway..
Problem is when they go back to their positions the wall edges forward again.