Well I will start with Corsair since it is a buffer and I am a BRD. I can see some awesome possibilities and some shit that SE probably will not allow. We do know Corsair will be capable of giving a JA of one party member to the rest of the party. I do not think these will be active job abilities due to the fact that giving everyone in the party Meditate or Convert might break the fucking game lol. Still the passive ones are interesting enough.
NIN - Dual Wield (situational but could be hot) and Subtle Blow (less worrying about melee TPing on HNM... would put more melee in alliances on stuff like Wyrms instead of BLM and SMN hopefully
WAR - Double Attack (hotness)
THF - Triple Attack (also hotness)
BRD - Resist Silence (poooooop in most situations)
DRG - Accuracy Boost (interesting for high eva mobs)
DRK - Attack Bonus (high def mobs)
RDM - Fast Cast (hot for mages, brd and utsu tankers since it is confirmed fast cast effects utsu timers)
BLM - Magic Attack Bonus (lol), Conserve MP (could be hot)
SMN - Auto Refresh (nice)
BST - Killer effects (not bad for tanks in some situations)
SAM - Store TP (yeah that would own)
RNG - Ranged Accuracy boost? (not really so hot)
MNK - Martial Arts skill? (crap lol), HP boost (hot for tanks methinks)
WHM and PLD I forget their passive abilities to be honest
I thought about this last night while drunk haha. Corsair could really own depending on how often you get the positive result and whether this shit is aoe and how bad the negatives can be. Still Corsair might replace BRD in some situtations, but this shit will stack with BRD songs.. which is hot as hell. What do you guys think? Care to speculate on Puppetmaster or Blue Mage? Sorry for the long ass post haha.