Con
Right now, no access to heavy armor. This is probably the saddest thing for me for mages *tear. Imagine a Thuamaturge in heavy iron armor. *forlorn sigh* And the greatest limitation.
Jobs limit cross class skills.
So,I think ^^TheodoreMcIntyre^^ probably has the best point on why it wouldn't happen, setting aside current equipment limitations pointed out by ^^Ceodore^^(curiosity is good). My counter to Theodore would be that a good tank could compensate for this, regardless if it's melee or ranged. In fact, a ranged tank could lead enemies into better position by running away and exposing the flank. A good tanker is good, a bad one is bad. How far they hit enemies is irrelevant. Though since it was mentioned, there are few, true ranged enemies, now that I think on it. Even magic wielding enemies seem to charge at your face as if to say "kill me, please." Odd.