I can easily see RDM coming to this game: Why?

Melee Caster DPS

Simple run down of how this class would work for alot of folks

Weapon : Rapier/Fencing style attack stance
Offhand: Shield or maybe a magic crystal? IDK still up to arms with this idea.
Armor: Cloth or light armor specifially for casters.

Skill sets: Magic
Now we alll know RDM is a hybrid class. between WHM and BLM with melee dealt inbetween. We also know that since FF1 that RDM has always used the EN Spells

Enspells: Any elemental spell that imbues weapon with said attributes with extra passive affects
Enfire: Adds fire damage to melee attacks and adds small BURN DOT
EnBlizzard : Adds Ice damage to melee attacks,also slows (or adds Heavy effect) Great for pvp or kiting
Enlightning: (a skill id love to see) Adds Lightning damage to melee attacks, Also shocks enemy adding paralysis
Enstone: Adds earth damage to melee attacks, causes Melee attacks to weaken the opponents armor by a certain % + stacks
Enaero: Adds wind damage to melee attacks, also increases your movement speed (or we could addd a slicing style aoe to the melee attacks like a small cleave)
Enwater: Adds water damage to melee attacks, may also silence the enemy

As far as passive abilites i can see them getting INT +, Maybe a little help from Armor+ passives to help them in the front lines of PvP/PvE

Cross Class abilites would be from either WHM/BLM or their classes.
The RDM is a hybrid so i can see them using any of these cross class abilities to help their parties out as well. Maybe taking healing spells to help off heal if the need arises. or Damage spells to increase their own dps.

I do not see them however getting their FFXI iconic skill Refresh since i think Bards mages balad is good enough.

Skills id love to see from previous games.
Convert: Switches HP with MP
Chaincast: Speeds up spell casting for a certain time frame
Haste: Increases melee attack speed by a certain percent.

The way this Class could work, i could see them implementing this into the armory system almost flawlessly.