Cam Banks said:
I like the notion of mystics as divine controllers, especially if their channeling abilities are used to create broader effects on the battlefield. In SAGA rules, mystics couldn't affect non-living things, but that didn't carry over to 3e. SAGA mystics picked one or three mystic spheres, depending on their Spirit attribute. These were things like Animism, Mentalism, Meditation (altering/buffing mental stats), Channeling (altering/buffing physical stats), Healing, and so on. So, while there's definitely a Leader sense coming from them, I'm not sure if that doesn't just make them a variant cleric or not.
The flavor of the Mystic makes it sound much more like the Primal power source than divine. 4e Sorcerers are probably going to be primal controllers, so a 4e mystic might work best as primal leaders. It would fit the role they seemed to have in the Saga flavor text and books.
The mystic is the only character archetype in Dragonlance that seems to need its own character class. The various knightly orders, and all the other major archtypes, can be done as feats and paragon paths. Mariners don't have much to distinguish them, aside from being lightly armored combatants with good skills. A feat or class option that gives Fighters a benefit for fighting in no armor would fit it.
To sum up:
Forgotten Realms: swordmage
Eberron: artificer
Dragonlance: mystic
Dark Sun: templar and/or gladiator. Gladiators would probably be martial strikers, whose extra damage comes from some sort of challenge or duel mechanic. I'd expect them to be proficient in heavy and light armor, and have lots of flashy powers that impose conditions upon the target. I'm not convinced that we need a gladiator, but it would be nice.
Ravenloft: archivist definitely. Ravenloft needs a scholarly Van Helsing type, who defeats monsters with knowledge and willpower.
Spelljammer: I don't think it needs a new class.
Planescape: Philosopher, maybe. Again, nothing comes immediately to mind.
Birthright: Magician. The magician was basically a 2e specialist wizard who could only cast high level illusions and divinations, and was restricted to 2nd level for all other types. If PH2 or PH3 has an illusionist class, it would probably fit it well, with some tweaks.
Oriental Adventures: Most of the classes could be done as variants on PH classes, new powers for them, and feats. Samurai are fighters, ninja are rogues, sohei are paladins, and wu jen are wizards. A Monk class is needed, preferably killing the swordsage and taking his stuff, so we can have effective armed martial artists, like in Hero and House of Flying Daggers.