Throwing out some ideas I've had for party support spells and a (probably overpowered) ability:
Float (25MP, Recast 1:00, Cast time 0.5 sec, Duration 5 seconds. Enhancing Magic, Party Target)
Prevents Severe Physical Damage (think Migawari, but limited to Physical moves)
Concept: Since RDM isn't getting Flash or Stun anytime soon , a defensive spell that requires reflexes to make useful that will be useful to both PLD and NIN tanks without completely eclipsing Migawari. The fun of stunning, but without removing any potential appeal of /BLM.
Subterfuge (70MP, Recast 0:45, Cast time 3.0 sec. Enfeebling Magic, Party Target)
Moves a negative status effect off the target party member and onto the enemy.
Concept: If unresisted, transfers a debuff from the targeted party member to that party member's battle target (same targeting mechanics as /assist). If resisted (some status effects will probably always be resisted on NMs, such as Petrify), has a chance to remove the status effect anyway.
Alternate Concept: Puts up a Dread Spikes-esque effect on the party member that transfers debuffs from the party member to the enemy each strike. Lasts for variable amount of hits, based on casting skill (similar to Aquaveil's variable number of interrupt preventions based on skill).
Suspend ((Merit Category 3?) Job Ability, Recast 15:00, Instant, Duration 15 seconds, Self Target)
Terrorizes everything (including mobs and alliance members) in range (30' Sphere) except the RDM for 15 seconds, but puts Amnesia on the RDM for the duration of the terror effect.
Concept: RDM is known for casting spells quickly; in this case, they cast so quickly that time itself crawls to a halt for everyone but them for a short duration. The idea is for an emergency JA used to try to prevent an incoming disaster, or to recover after a devastating attack against an alliance, but as it's meant for casting spells, not to use Job Abilities (and to prevent Suspend + Chainspell abuse), justification can be that JAs can't be used when time has stopped. The terror effect should not act as a Stun against enemy TP moves being readied when the JA is used (they should go off as normal when the Terror effect ends).