Possible Flarm transmit stealth mode

I woke up with an idea for another way to do stealth mode which might be less vulnerable to hacking. Not sure if it's useful but seemed worth posting for thought.

In the current system, each plane periodically broadcasts it's state vectors (lat, long, alt, id, and stealth flag), and the receiver implements stealth by filtering out stealth flagged non-threats before display. The state of all planes is available to any hacked receiver.

What if instead, the normal tx mode was to only broadcast lat. Then if the local rx heard anybody near that lat, also start sending long. Then if it heard somebody near the lat+long, start sending altitude.