This weapon thing isn't that big of an issue. You can already have 1 and 2 hand blm/whm/thaum/conj weapons. They could have 2-handed gladiators' or "daggerclass" arms that are Katanas. The stats (and lack of offhand in the case of glad/paly) would make it pretty clear which Job was supposed to use it.
The bigger issue is the body skills learned by that class.
The thing about a third tank is that it has to come from a base class that isn't gladiator or marauder because you want the jobs to add type-variety. And I think its easier to turn a tank class into a dps job than the other way around. Having only 5 skills come from the job makes it pretty hard to totally change a class's base usage anyway. Sch/smn work, in large part, because they changed the pets - and that they mixed in a couple healing skills in the class. The others don't currently have much of that.