I feel like the idea that SE can't design a new job is silly. So I guess this silly feeling is mutual :P. I really dislike the arguments of "but it'll just be BLM/SMN" like SE is incapable of designing something unique beyond what they've already done :/. SE can design a new mage, I'm certain of this.
I find that if they took the current setup of insert color of 130 potency skill that Blue Mage would be boring, so I'd also rather have a two job system where the limited side is unbalanced and true (or at least "exaggerated") to the original spell and the "main job" side is balanced and follows it's own rules for gameplay mechanical fun. I'm not a fan of the heavy amount of Blue's duplicate potency different color issue and I wouldn't want to see it become a core feature of the job to make it work.
So while your idea is certainly straight forward (massively so, blue mage a normal job by next week sort of levels lol) I guess we'll diverge there as I think Blue Mage isn't in a good place to take the simple route (nor can it be, imo, because "130 potency of X color" feels bad now and I think will feel bad in the future too).