The trouble is, I don't know how this could fit in the current idea of the Armoury System, where there is specific separation between melee classes (Disciples of War), and caster classes (Disciples of Magic). Red Mage is a jack-of-all-trades, master-of-none class, it has reasonable attack power which veers into the mediocre eventually with the ability to cast both White and Black Magic, while not excelling in either school of magic.

And because in FFXIV Job skills (i.e. Black and White Magic) are not shared cross-Job, it means Red Mage would not be able to use only get it's own unique skills in addition to a few cross-class spells (presumably from CNJ and THM) which kind of destroys the whole concept of it even being a RDM in the first place.

Hence, I doubt you will ever see RDM in FFXIV for this reason alone (and before you pass judgement, FF Tactics had both BLM and WHM but never had RDM either - at least, not the original FFT anyway.). But may Yoshi prove me wrong though!