Flash has a 100 potency to it, which scales off your attack stat. (its why flash generates more threat for a WAR in zerk than a PLD in flight or fight. Its also a magic spell, and subject to spell speed.)
So the modifier is still x6.
Its better to assume unleash might go from a x6 threat modifier, to a x12 modifier, to match its current threat generation.
Which I'd be plenty happy for, AND it will help teach newer players to rely more on abyssal drain for DPS.
Just for clarification, WAR generates the most threat for AoE, as it has 720 threat, instead of DRK/PLDs 600.
DRK wont really worry about managing TP liek WAR does, and DRK also wont be worrying about MP liek it currently does come 4.0 (you practically cant remove darkside, as you wont be allowed to hit dark arts w/o having the MP for it, and u only need MP for when adds spawn mid fight, which you'd need to know about before hand anyways.)
PLD will currently be the "all rounder" as it handles physical and magical dmg equally, and can mitigate them more often than DRK or WAR can.
Its current magical attack DOES require you to watch your MP, as your dmg will go down below 80% mp for one of your CDs.
So my guess is;
WARs will worry about running out of TP in AoE threat, with some worry about wrath, for free AoEs.
PLDs will worry about MP for single target DPS.
DRKs will worry about saving some emergency MP for an AoE in case of adds spawning mid fight.
WARs wont worry about single target much.
PLDs wont worry about AoE much (except to throw in more DPS with their new AoE, which drains TP)
DRKs wont worry about... either very much, as their rotation is now "When its up, use it."
EDIT: DRK does need to make sure it has MP saved for Carve and Spit, or Dark Passenger. (picking Carve and Spit before Dark Passenger if limited on MP)
EDIT: lol. Technically if you have a WAR, NIN, or SAM, then dark passenger has a power priority in use than your GCDs.