Just to elaborate on some of my reasoning:

Paladin: PLD would still be the lowest burst dps and lowest AoE dps of the tanks by far, but its sustained dps/enmity would be more competitive and Clemency/DV would be more useful.

Dark Knight: would provide a more interesting choice when deciding whether or not to use DA on C&S and make Living Dead a little less of a pita.

Warrior: BB combo would be the same potency as SE, allowing them to not have to spam their enmity combo while OT for dps. Things like Tetragrammaton and Lustrate would work with their tank stance.

Ninja: Their max dps would not go up at all, but they would suffer less of a dps loss for not having a Warrior around to use the slashing debuff.
This would make raiding with PLD+DRK with a NIN less punishing. (Making WAR less mandatory)

Bard: Bard gameplay wasn't originally designed for cast times and plays really clunky with them as a result. This change would accomplish the same thing as the current WM, Allow the Bard to increase its dps if it doesnt move, but without the clunkiness. It would also differentiate gameplay a bit between Bard and Machinist so that they aren't so similar.

Whm: They are the only healer that doesn't have attacks which ignore accuracy, so giving them a bit of an ACC bump in Cleric Stance seems reasonable.

Blm: 12 sec would allow just a little more wiggle room for movement without the rotation getting severely borked, but its not enough of an increase to allow extra Fire casts in AF I dont think.