Looks like a case of 'what's old is new again'. Similar to the old copy protection used by Atari etc. Cheap and easy to implement but hard to overcome by the consumer. Be thankful for small mercies if that's the case, because at least additional maps work (mostly).
Of more specific interest would be if someone could say just how the Goldwing fw now enables those units to read NT maps, and see if that can be used in other older 'non-NT' units by similarly modding their fw. Of course if the GW units already had that ability built-in and it was simply 'unlocked' by the newer fw then this is of no further use if other older hardware is lacking that, presumably. But what if it has some sort of NT de-encription built into the fw? Sounds like a job for a bright but bored young expert .There are plenty of bright ones around this forum, but are they bored enough??