I want to keep being able to level up anything, anytime, to any level I want it to. That's one of the strength of the armoury system, let's keep it that way.

As for "mastery" of a single craft class, the idea behind mastery should be defined first.
If it means being able to level up all my classes in Discipline of the Hand to 50 and then select one as "master" where it receives extra bonuses, I'm fine with it.
If it means I won't be able to level up all my classes to rank 50 and only the "master" class in Discipline of the Hand will, then I'm against it.

If they want to limit the numbers of items in circulation, control the economy of synthesis or whatever, it should be done by building new features over what we have, not cutting existing features. The more freedom and dynamic content, the better; not the other way around.