After my suggestion/rant on puppetmaster and geomancer, as well as mimic, I've been thinking of other neat concepts.

I've seen chemist as a healer thrown around a lot, but never figured out what could be done with it overall. But after some thought, I feel it'd be fun if it had a system similar to Ninja with ninjutsu, but instead of combining hand signs, you'd instead combine ingredients into your flask, to make different effects. This way, A + B = Z, A + C = Y, B + C = X, and so on, and then using the Throw action, you could use whatever effect + heal you concocted, it could be heal + damage (like some healers already have), heal + buff (like regen), or even a combination of ingredients that instead changed a solo target move to an aoe move. I think it would add something more unique to the table.

As for another idea for tank, I was thinking how Nero's hammer weapon was never really explored. It could be interesting to have a Hammer that turns into a Cannon, and use something similar, albeit slightly different to gunbreaker, in terms of changing your weapon between cannon and hammer, and call it perhaps Cannonneer, since that's already a term in FF.