Chemist using a gun is pretty unlikely. Whatever it uses is going to use melee weapons (like the others). They aren’t going to give you a weapon that breaks the balance of auto attack, and a weapon that looks like a gun but can’t fire would be extremely misleading, which would upset people.

As far as using elements go there either isn’t a healer that does (if we mean attacks) or all of them do because of aether colors, so that’s kind of a moot discussion. It’s also entirely possible Healers will get expanded offensive options again.

For Green Mage not sure they would go that road. While Summoner certainly has issues (books not being one of them though) it’s still not completely dissimilar. I suppose they could combine a druid vibe with status effects though. Green Mage being pretty simple in concept they could do a lot with it. That said I would think more of Oracle/Mystic if I was thinking of Green Mage variants, as it’s basically that job but with aesthetic quirks.