Need more info before I'm entirely certain but I think I'll still want to see a transforming based job. Reaper may have that, maybe not. Going anime super power bleach mode isn't really transforming imo. Which isn't to say I don't find the job interesting, I'm totally going to level Reaper and I think it's going to be a lot of fun, and looks cool so far, the comment just being I don't, so far, consider it a transforming like job.
I would toss my table and fan scream if Reaper ended up being able to go Diabolos like mode though.
If Reaper doesn't have that element an Esper (the Zodiac "primals") would be a cool transformation theme'd job, potential inspiration also from the new FF game I think- as it appears to have not exactly transformation but at least imbuement / near cohabitation of space (though upper levels of the job I'd still want full cohabitation, not partial). While anyone, I think, who wants a transformation job knows that too much customization is difficult (like those who play Druid in WoW are used to not having their armor set represent), I do think you might be able to come up with some level of throughput. In the dark transformation job thread I suggested cloaks, scarfs, sashes, and the like as the weapon. Then design the transformations with intentional space for this weapon to show up on the body. Like if you imagine a wolf transformation (big wolf like Sif in dark souls) then your cloak you're wearing might show up as a big similar cloak in your wolf mode. Relics might introduce minor further customizations like the wolf becomes elemental / other effects or texture tweaks (like if the weapon had some blood moon history then you might leave darkened foot prints have glowing eyes and a smokey red aura of power with a minor tinge of red to the fur, being a special tweak for that relic). I just picked wolf randomly as an easy example, obviously epsers wouldn't be animals like that, though I would be fine with an animal based transforming job too.
I like the Geo Knight idea formed over a few threads- a Golbez, Ex-Death, Suaron (LotR) inspired heavy bruiser mage job. No elegance, very aggressive, everything is crunchy, like fist punch to the face fire exploding out in a huge torrent, clench fist upwards causing earth to pillar through enemies, hands clawed towards each other causing a huge orb of water suffocating and raising an enemy in the air (raised if stun debuff applies, otherwise just orb over enemy), might pull one hand away while the orb is formed and call lighting down like zeus and pierce the bubble. Weapon might be a two handed mace (with perhaps a bell built in). Originally I had thought of elemental pylons, but seeing as we've sage now I think that's a bit out lol.
I'd love to see holy element used in a more aggressive manner as well. That might just mean some more Paladin spells but currently the major holy spells in this game are fairly regal (like snowflake appearance to Paladin's holy magic). Some inspiration from Dark Souls holy magic, Crusader from Diablo, perhaps the bible old testament (with all those anger moments and wild angel looks).