Flarm currently does not have to ensure compatibility to its legacy code (due to mandatory updates), let alone having to respect a protocol or the ideas of other vendors. In my opinion this flexibility is one of the reasons Flarm was able to evolve so well.

Opening the protocol would mean that all stakeholders would need to agree on any change to the protocol. New ideas would need to be formally filed, debated, different interests negotiated, compromises would need to be found before a small change finally can be implemented and rolled out. Unfortunately democratic processes are not very efficient. Looking at the ADS-B discussion in another thread shows how difficult and time consuming it can be to establish a new standard.