The armory system is pretty straightforward...Yoshi's bringing the classes inline with his vision of the game, which is a MUCH better vision than the original by far. Currently, the jobs are going to be 1:1, but since they're items (Job Stones) then this won't or shouldn't always be the case. I could see Marauder going Warrior and Dark Knight for example.

Put down your 'The End is Nigh' signs and play the game. Changes are coming, and we've known about them for quite a long time.