I'd still rather focus first on diversifying the jobs we have, with the support of far greater alt-job-friendliness.
Pick some 2-4 core aspects of each job and build them out.
Start with creative limitation, such as having only 14 buttons with which to make a fun job kit, and ensure the new skills add onto and kind of celebrate that earlier kit instead of just trying to patch out its integral weaknesses (for which its compensatory strengths were given) and undo whatever mechanics were put it prior (old RoE in place of positionals, Barrel Stabilizer just to undo Heat, etc.).
Who knows, we might then even be able to get jobs that actually play pretty decently even before level 70.
On a complete pipedream side, though... screw jobs as the be-all-and-end-all. Give us some manner of mix-and-matcheable paths instead, with various subcategories. BLM, for instance, might tap into Evocation and Invocation, Umbral Magics, Meta-Magics, and Ancient Magics, with Lightning and Fire as a subset of Umbral Magics, itself a subset of Evocation, etc. A NIN might use Subterfuge, Shadow, Wind, Fire, Onmyo, etc., but could draw also from neighboring paths. Subterfuge would also tie into GNB, for instance, Wind into CNJ/WHM, Fire into BLM, Onmyo into GEO, etc. Want a goddamn Fire Ninja? You can have a goddamn Fire Ninja. Wind Rogue? Have a Wind Rogue. A Ninja who specializes in Onmyo and Planar magics to form some manner of Warp Blade? So be it; it'll probably be niche as hell, especially outside of some Arcanist-Astro comp, but have at it. Rogue -> Ninja would just be a weapon type with some natural synergies, anchoring animation style and core stat scaling, and its own path of skill acquisitions, but little else constraining it. Go ham.