Just some silly ideas

Red Mage Tank

Weapons: Rapier (Piericng), Shield
Cross-class: Conjurer, Thaumaturge

Magic Sword stance, Elemental Ward stance

Magic Sword - Increases accuracy and also increases the potency of both auto-attacks and weaponskills by 30.
Elemental Ward - Decreases damage taken by 20%, increases enmity gain, increases elemental resistances by 10. Elemental resistances are mostly fluff, but people like fluff and it's different.

En(element) - Instant cast abilities that share a recast timer, each provide a unique power depending on stance. For example, Enblizzard could put MP steal on attacks in Magic Sword stance and in Elemental Ward, it creates an aura of cold that reduces nearby enemy attack speed.

Tankbuster Buster = Reraise. Spell, instant. 4 min cooldown, 12 second duration. When killed under Reraise, recover full HP and gain 30% damage reduction for 6 seconds instead.

Dualcast = 3 min cooldown, 15 second duration. Your next spell is cast a second time 6 seconds later for no MP cost.


Possible spells:

Dia - Ranged pull?
Muddle - Spell-type Provoke clone
Saber - Spell, three second cast time. Increases own attack power by 15%, duration 24/30.

Notes:

Spells with actual cast time to make Swiftcast and Surecast both good picks. If only Raise didn't need a trait to be used in battle. Could you imagine a tank with a battle res? Probably a waste of a slot to give red mage its own raise spell though.

Needs an MP use mechanic that probably isn't constant drain like DRK.