Well, if I could design it, I would have it play similar to 4.0. Umbral and Astral AF would charge the Aetherflow with respective elemental gems. Then each elemental type would dictate a certain DPS play type and would also be a minimum of four attacks instead of one. The primal summoned would stay out for the duration of the 15s doing an AoE 2.5s auto attacks, so during pulls it's not useless like Automaton Queen. SE could even give them a preset cast order to mix it up. However, I would make them "small" as default, use only range attacks, and scale back the Enkindle's flashy graphics (Titan!!) so it doesn't disrupt other players.
*Earth/Ice would be you quicker cast (1.5s) combo but with more than two buttons similar to your melee combo setup. (Example: 1 > 2 > 3, 1 >3 >4)
*Fire/Water would be your longer cast time spells with more variety based on the primals attacks (Ifrit Example: Incinerate, Crimson Cyclone, Eruption, Sear)
*Wind/Thunder would apply 3 DoTs and a casting spell (Aero/Thunder are DoT spells after all).
*Note I said cast meaning it needs a cast timer, not instant cast. IMO caster rolls should stand still and cast spells. Physical Range should be the run and gun jobs.
After the Umbral or Astral gems are used up you can cast either Bahamut (Umbral) or Phoenix (Astral). Give each a 1 > 2 > 3 combo with 2.5s cooldown. Change Bahamut Enkindle to Megaflare because two Akh Morns is just silly at this point. Change Rekindle to Revelation and make Flame of Rebirth Phoenix's Enkindle. Next, I would have Everlasting Flight changed to a large AoE Regen Circle which is cast at the target. In respect, Bahamut would use Shadowflare, a large AoE DoT circle which is cast at the target.
You can also toss on some abilities to help round everything to include summon type animation attack like Susano, Odin, Alexander, Bismark, etc... (don't need to replace carbuncle just for a spell animation).
Edit: Now this is just an idea of trying to blend what worked in the past with what people want the job to be in the present. I don't think SE is going to do anything other than add another pretty ability or two, keep it a two-button job, and pat themselves on the back for it. Rightfully so, sadly, because it seems people want a simple as can be job that a Drinking Bird Desk Toy can perform.
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