Doesn't help one iota. The relay attack uses a two way amplifier to effectively increase the reach of the frob. This way the evildoers can steal the car while you are sleeping.

As tropo suggests above, it would have to measure the distance (signal propagation), but I suspect that would drive the cost of the frob up significantly.

EDIT: to be clear, this isn't the attack discussed in the article, but a more serious problem that is already in use today.

Sorry, I mistook your point.

The critical issue for rf keys is the lack of a button to lock/unlock the door.