In every FF game Chemist has shown up in, it has been a very fun and interesting healing/support class. Mixing items to create various effects, anywhere from powerful healing effects like full party revives, powerful support effects like increasing the character's level by a whopping 20 for the battle, or powerful offensive attacks like Shadow Flare. FFT's Chemist allowed them to also wield a gun and shoot from far off, giving it a nice long range offensive ability compared to its original appearance in FFV. FFX-2 added an interesting layer in the form of the Stash abilities, where the (Al)Chemist would pull out a hidden item for use that was not counted as being from your inventory.

From those, we can already see a few ways that Chemist can work in FFXIV as a healer. Wielding a special gun that could shoot alchemical effects, giving it a long range weapon for using its skills. Mix would allow it a Mudra-ish system allowing for multiple interesting buffs and heals to be created depending on the mixture. Stash would easily allow for oGCD heals, with you throwing out hidden potions you had kept on you (in places not even the player knew about) to heal your allies or damage your opponent.

Also originally the dev team had planned on adding Chemist for HW but couldn't figure out how to set up the mixing system right. Chemist was tossed out for that reason, and the system was used for Astrologian instead. Judging from how they've figured out how to use the system better since then (see Mudra changes and Dances), Chemist could be back on the table.