The problem with that is if you fly online on VATSIM or something, if an air traffic controller gives you clearance for take-off, they expect you to take off, not sit there and delay everybody else. Additionally, it's usually the air traffic controller that would tell you that a vehicle was on the runway, and if you're using default ATC, they would have no way of knowing that a vehicle was there since GSX doesn't interact with air traffic control in any way.
