I think that people who are looking for a new healing job are looking for something that offers a different experience from the existing healing options. I think that the idea of 'mixing' effects between potions and/or toxins (in the same vein as Bravely Default's Salve Maker) is a good idea.

One way to do this is to play with ground effect fields. Let's say that you throw a potion at someone, much like FFT's chemist. There's an upfront heal to the target, as well as a heal over time ground effect field that heals up anyone who stands in your healing puddle. Let's say that you throw a second potion. That then interacts with the 'over time' effect of the first if the fields overlap. So as an example, let's say you threw a Potion, followed by a Hi-Potion, and the two fields overlapped. The heal-over-time effect might be enhanced. Alternatively, if you thew a Potion, followed by a Grenade, perhaps the field ignites, with healing over time for your team and damage over time for enemies standing inside.

As far as resource systems are concerned, I think it would be interesting to play with a system that was more cooldown dependant than resource dependent, especially with the 'charge' system available for some oGCDs. You could create a healer that wasn't reliant on MP at all. Also, don't forget about Auto-Potion. That almost certainly has to show up.

I think that there should be a limit placed on resurrection effects across all healers. Phoenix Down can be a single target rez, but there should be a shared number of uses per fight across all healer equivalents.