This has been such a pain for so many years. Braking action, braking coefficient, medium or medium good...and so on.
Contaminants of different types and depths across a specific percentage of the specific runway length...phew....what an equation.
IMHO TALPA has done a good job with the RCAM and the RWYCC's in an effort to unify procedures and above all KEEP IT SIMPLE.
It's not a perfect system but, it gives a good picture to the flt crew and then takes into account the PIREP....Braking action only derives from the crew that handles the aircraft.
In 2019 3 Scandinavian airlines, operating Airbuses will have the Braking Action Computation Function (BACF), Results will go through ACARS into NAVBLUE and everyone will be happy