Very interesting seeing how this attack is performed. I'd imagine that future keyfobs would use a time of flight based system of call and response to prevent this sort of thing.
Keys are sometimes set down in the vehicle before starting. A time based rule (motion within last x) won't help because sitting in a non-running car is something that happens often enough that keys not working would be a problem.
Also, someone could steal your car while you have your keys in your pocket inside your house, or walking around a store.
This was a relay attack. Not a re_p_lay attack.
It's just amplifying the signal from the outside car to the inside keys & vice versa.