Here is how I think it's supposed to work.....any mage CLASS is going to be like being a red mage since CLASSES are supposed to be less specialized than jobs. When you equip a JOB crystal, you stop being a "red mage" and specialize into either White or Black mage for example. So IMO Red mage is already there.... sort of.... people just don't see it without all the red getup on. Level all 3 mage classes, pick one, stay CLASS and not job, and swap in some abilities. Perhaps then you'll have your makeshift "Red Mage."
I just hope that in some situations (like soloing for example) classes turn out being more useful than jobs,else they should just get rid of classes all together.
I haven't leveled much mage yet, so I could be full of it, but I think classes are supposed to be the jack of all trade red mages.