This popped up over in a thread in the FFXIV forums, when we were discussing different directions XI could go for dungeons.
CTB was a great deal of fun in FFX. For practical reasons, it makes more sense in an MMO to have a real time/active turn based system for regular fights and the majority of content.
But what about in a special dungeon? A party of six could enter the battlefield, and suddenly be locked into a conditional turn based battle against a monster. Turns could be calculated based on the weapon delay for melee and fast cast for mages, with Haste and March as modifiers (and slow, too.). Instead of a hard time limit, each player could be granted a quantity of turns (say, 20) and the monster they are fighting has a set quantity as well.
This would stop the standard "zerg rush" strategy that players are so fond of, and force us to use our heads, set priorities, and think about how to defeat the monster - especially if it's susceptible to skillchains and magic bursts (now there's a really fun way to bring those back!)