The scout, which someone mentioned, would bring ranged sneak attack into the game (more effectively), but there's problems. First off, scouts only get extra damage while MOVING and shooting. Combat would be worse than the Blair Witch Project for motion sickness. Forward, back, shoot, forward back, shoot, forward, back, shoot, etc. If you change it to simply standing still and shooting, you're getting rogue sneak attack damage without the threat of being in melee. Also, scouts get rogue skills as well (DD, search, etc). Why play a rogue anymore?

What I feel DDO could use, rather than yet another damage dealer (including warlock), would be another healing class and a tank type class. Druids can be very effective healers, and using DDO's mp system, they'd probably be as good as clerics/FvS. Druids also bring entangle (one of the best CC spells in PnP, and it's a first level spell), some pew pew laser spells, buffs, and could possibly animal form tank/melee dps. Personally, I always turned into a bird and cast spells above the battlefield, but whatever floats the players boat. This would also greatly improve gameplay overall, because many groups have problems finding a healer. It's a VERY diverse class.

For a tank type class, what about the Knight? Effectively an intimitank, they get d12 hit points, armor and shield specialization (furthered by in game enhancements), and I believe high fort and will saves. Just a thought.