Spontaneity is exactly like WHM's Presence of Mind so that's technically taken.
Composure was kind of a band-aid buff in FFXI, it didn't actually solve any issues and only applied to buffs casted on yourself till the AF3 came out. There actually was an ability that extended the duration of the spell in FFXIV (Can't remember the name of it for the life of me) so it could work well if RDM got it's own buffs, the only problem is without RDM getting it's own worthwhile party Enhancing spells, anything we cross class from WHM or other jobs would be at half strength because we would lack trait enhancements.
Trainquil Heart I could see working well, but it's a trait so I dunno where it would fit especially if they don't give RDM any of it's own healing spells.
I loved Phalanx that could be a workable spell, specially if you can stack it with Sacred Prism and if they included a enhanced duration ability. It would have to be named something else though since GLA has a shield move named Phalanx.
Gain spells, I could go for that too long as it buffed numerous parameters and was adjustable with Sacred Prism. I'd hate to see it be single target, take up an entire bar for each stat, and just have to relive the cycles... the.. Cycles... OH NO... IT'S HAPPENING AGAIN!!!! GO AWAY GO AWAY GO AWAY! *Hunkers in a cradled position in the corner holding my head shivering*
Temper was one of those spells that was too little too late for RDM, after years of ignoring RDM and it actually being so under-powered and pigeonholed to the point they didn't even want it for the mage aspect anymore Tanaka just threw this out there to try to shut the melee crowd up (and enticed the rage of the anti-melee crowd many of which didn't even care about RDM anymore.) It could be useful as a JA that increases the speed of your attacks, attack power, or double attack depending on how SE want's to play with it, definitely something to consider though.