In a sense paladin is already the anti red mage in that regard, mostly fighting in melee but during the requiscat part of their rotation turning into a caster, then going back to melee.

I also don't feel it's generally going to be a dynamic as red mage because you don't need to move around do the ranged part. RDM it's kind of cool to be at range, zoom in for melee and flip back. In the opposite, you would generally just stay in melee during the ranged part of your rotation anyway because you never 'have' to be far away to use a ranged attack/spell. It would just be a small convenience being able to keep up that part of the rotation when a mechanic makes you run away from a boss for a few seconds.