I was involved in a conversation about healer role that got a lot of thoughts going, and I wanted to share them all at once. There are a lot of things in the game that could be taken as inspiration for future changes, especially now that the PVP actions are out and everyone seems to find them refreshing.
SGE has something similar going with the addersgall and addersting stocks, and I think that can be improved if they make Toxicon more rewarding to use and acquire, or perhaps expand the Addersting mechanic. I've found that outside of dungeons, going out of my way to replenish Addersting is something of an opportunity cost, since they are only acquired from depleted single-target shields, and that doesn't feel like SGE's identity. Perhaps the player could also acquire them from increments of healing applied to missing HP by Kardia? I feel that rewarding players for using Kardia proactively would make the job more engaging. I also think Pneuma, while the mechanics are fine, needs like a visual upgrade that makes the giant laser even more impressive. The effect flashes for a split second and is gone!
SCH has a very powerful ultimate ability in expedient, so much so that it was nerfed. However, the fairy gauge feels like it is missing something at the moment, as aetherpact is the only way spend the gauge, and there is no particular reward for spending gauge other than additional healing. Perhaps they could apply a gauge cost to certain fairy actions while also awarding a new gauge value that either powers up Seraph mode, or even gives SCH an offensive tool, such empowering broil or reducing the cooldown of (or adding charges to) Chain Strategem.
AST...well it's understandable that the job is in a strange spot. Every player I've spoken to that mains the job feels like the card system is too simplified now. Perhaps we could lean into the YugiOh memes and take some mechanics from trading card games. Maybe implement card combos (and to save player brainpower, the combos could auto-complete), to add a semblance of summoning Exodia. Give AST a reward/consolation for discarding a drawn card, or even create a playstyle where the AST sits on a situational combo while using discard self-buffs to bide time (such as acquiring stacks of the double-cast skill from PVP). Even making it similar to mahjong could be a neat idea.
WHM is in a reasonable spot, but a lot of people seem to think the healing blossom is difficult to utilize. I think tying more things into the job gauge could help. The blood lily system is rewarding, but there are definitely certain times when things are going TOO well and there aren't any good times to spend lilies. This could be helped by simply making it more similar to SGE, where lilies can be spent to empower more spells.