Predictions for job(s) in the next expansion?

[Archwizard]

If things are done right the Rune Knight may end up as a Range Caster Class. Maybe the first Caster class that focus on pure instant cast spells from range by swinging their swords to create elemental Slash Wave attacks

No Red Mage does not count as a Pure Instance cast spells Caster because they still need to go through the process of Casting spell 1 before instant cast spell 2.

1. That would be wildly imbalanced. Not having any limitations on range OR cast-time means there is no reason for the job to ever stand still or skirt a PBAoE, which would give them ridiculous amounts of evasion.

2. A Rune Knight, Spellblade, Mystic Knight, etc. job has historically always been a Physically-oriented job with an enchanted weapon, inflicting magical debuffs as a function of its melee attacks. At best we would see an implementation with full melee combos leading into instant spells, but not a ranged job based around firing energy waves from their sword (particularly since SAM, GNB and RDM already have such an attack). As with RDM, if they're gonna give a job a sword, at some point it's gonna be used for stabbing someone or else they could have just given them a gun instead, and RDM already has the range-into-melee-burst rotation covered.

2a. ... and much as I might like to see a Spellblade, I have no reason to expect a melee job before we have a fourth healer, physical ranged, and full-caster.
2b. ... the exception being they implement a new role like "Magical Melee DPS", or shift NIN over to a physical ranged job, in order to make room for a melee. Neither of which I find likely any time soon, since the former would be a nightmare to balance and the latter is kinda late.

3. There are still plenty of untapped options for actual casters (hell, we have SMN pulling double-duty as the DoT caster and only Pet job, and it does precisely neither of those to anyone's satisfaction), without dipping into implementing jobs entirely outside of the role. GEO happens to be the front runner in that category.