Beta first thoughts.
In response to the last paragraph of your post – When HoT launches the masteries will be seperated into 2 ‘groups’: Heart of Maguuma (Gliding, Mushrooms, Lore, etc.) and Central Tyria (Legendary Precursors, Pact Commander, etc.) and you can only level each type of Mastery track based on it’s location, i.e. Heart of Maguuma will only be able to be leveled in the Heart of Maguuma maps, aka the ones that come out with the expansion (and presumably Dry Top and Silverwastes). Similarly, Central Tyria lines can only be leveled in the Central Tyria maps, aka all the other PvE maps that Heart of Maguuma doesn’t cover. Hope this helps!
“If we do not end war, war will end us.” -H.G. Wells