If they did add Musketeer, I would assume Corsair would end up being the first Job.

But if it came with a second Job (like Arcanist does), I would really love if they gave it Chemist (as a healer). Chemist's in FF Tactics used guns, and it would be nice to add another Healer, especially a non-magic based healer. They could have heals like "Tonic" and "Remedy", as well as having a "Mix" ability that would let you combine two of their "spells" to get a new effect.