SACTA v NAS is a none starter. NAS can handle the entire OLDI message set which goes way beyond PAC MAC & REV. NATS chooses not to spend the money on NAS to introduce additional functionality. Be aware though that its no good having all this functionality if the adjacent ACC's don't. I agree its time for NAS to go but only when the replacement is able to support the traffic levels. SACTA can? is Scotland/MACC but not in London, hence iTEC. Interoperability through european co-operation. Or, SACTA enhanced. Its safe to say that most controllers have a fairly limited understanding of their FDP system and that's the way it should be.
Forgot: PAC will be introduced in support of the NAS/SACTA split. PAC = Pre Activation Co-ordination. REV is a revision message and MAC is basically 'I aint commin'