Chemist.

Been wanting this since FFXI actually... Could branch off of a starter job like the Musketeer that's been discussed. I actually made a tabletop FF game for my hubby's b-day (It's essentiallly in 'beta' right now still testing things out) and I think the concept I had for CHM could easily be translated. Granted some elements I have are tactical and would have to be translated but... here is what I have:

Chemist (CHM)
Stat Growth Per Level Str 0
Vit 0
Dex 1Spd 1
Mag 0

Abilities By Level
Level 1 - Mix (Gives the ability to create certain combat only items) (Active)
Throw Item (Can use an item on an ally that is within their movement) (Passive)

(Continued...)

Level 5 - Pharmacist (Double effects of potions and healing items) (Passive)
Equip Gun (Passive)

Level 10 - Hurl Item 1 (+1 square/hex to Throw Item) (Passive)
Auto-Potion (Use a healing item at no action cost when at 25% or less HP) (Passive)

Level 15 - Ranged Attack Up 1 (+10% R. Atk) (Passive)
Move Find Potion (10% chance to find an item normally created by Mix (GM’s discretion) per one square/hex of movement)
(Movement)

Level 20 - Revive (Brings back one ally from unconsciousness at 25% HP/MP) (Active)
Hurl Item 2 (+2 square/hex to Throw Item) (Passive)

(Further Cont...)

Level 25 - Ranged Attack Up 2 (+20% R. Atk) (Passive)
Potent Mix (Items created with Mix are 20% more effective) (Passive)

Level 30 - Hurl Item 3 (+3 square/hex to Throw Item) (Passive)
Mega Mix (can make double the normal quantity of items with Mix) (Passive)

(still cont...)

The stats are due to them using guns.
In mix I have some debuffs (i.e. Berserk, dud potion which is a random debuff) Some buffs (haste, regen) and some damage (Drain, non-elemental dmg) I see it as being support-dps. I would explain further but... character limits x.x
Mix requires mp to make the consumables, in tabletop its one round to make them and then they can be used, you can carry them on you but they are CHM only items.

If you're thinking about it, why not steal from RO?

They had a great Merchant -> Alchemist and Blacksmith -> Biochemist and Whitesmith (clearly this was some racial white power thing here lol).

TBH, I would LOVE to have RO classes in FF14. RO had great class design!

Also, acid demo was an amazing tank killer, and cart term was a great dps killer.

EDIT: ALSO THEY HAD ADORABLE CARTS WITH PANDAS ON THEM OMGGGGGG