I like the Chemist idea if only because throwing and combat mixing are some of the few staples of the series that aren't anywhere to be seen yet. I think that it might be best for their "items" to be mostly flavor though, represented by buffs/job gauges. It'd really suck to run out of something in the middle of a dungeon or trial and feel like you have to abandon if that causes a wipe. I'm thinking using something similar to Mudras to "stock" and mix items from an infinite supply of basic reagants.