This is very similar to FLARM devices (https://en.wikipedia.org/wiki/FLARM) for ultralights, gliders, etc. This is already broadly deployed (at least in Europe).
You could check for any lessons learned there. I think you can discount any flight users, because they would like to be seen too by other airplanes.
FLARM is very bad example especialy for DIY community. They have proprietary chips, firmware and are running non opensourced protocol. Also they are actively trying to prevent reverse engineering with cryptography and killing old/diy devices with protocol timebombs...
You could check for any lessons learned there. I think you can discount any flight users, because they would like to be seen too by other airplanes.