I have a little pet theory that the elemental classes will fall along role lines (at least a little), however.
Earth = Defender
Water = Leader
Air = Controller
Fire = Striker
I don't think so and I hope not. I'd much prefer for all of the elemental classes to, more or less, have access to a variety of elements each, though certainly they might favor one or the other. 3-4 common damage types, at least, for different builds and concepts. Also, I'm not sure that the classic elements are the way things will work out, anyways, since D&D relies more on Fire/Lightning/Thunder/Acid/Cold for the most part, with a bit of Poison and Force thrown in, when it comes to grossly physical effects.
I much prefer to see the elemental classes focus on using each element in a different way, such as:
Fire Defense: Fire damage when marked and not attacking the marker, fire-themed power, speed, or defense increases ("tempering"), explosive sliding attacks.
Fire Control: Smoke screens, walls and pillars of fire, magma traps, suffocating ash bursts.
Fire Striker: Set a foe on fire, further hits cause escallating fire damage and make for easier hits, ash in their eyes so they go blind.
Fire Leader: Adding fire damage to allies attacks and blazing trails behind them as they move, providing fire resist, giving them breath weapon attacks.