Just as with using AM phone on common frequencies to allow all in the vicinity to listen to and be aware of traffic local broadcasts I consider related data transmissions should also be transmitted en clair (ie. an open protocol) so that all can receive such information regardless of the make of their equipment.
There can be problems with this if too many vehicles in an area are transmitting, you can actually saturate the receivers ability to decipher all threats. What happens after saturation point probably then defeats having the devices broadcasting. A bigger question is how to avoid these events happening in close proximity to airports, naturally it's where aircraft converge and there are many limits to what see and avoid can do, even in controlled airspace where you are given traffic many collisions have occurred between known traffic, some with ACAS. Just have to watch the warbird collision in the US, should never have happened but it did. The biggest cure is orderly traffic flow, so everybody is doing what they are expected to do. Most collisions occur near a field when somebody is doing something not expected in the course of departing or arriving. I'm all for ACAS but its only one defense and a last one at that after all others have failed.