The undead class does sound cool :-)
But I think I know where a new race would head. If anyone follows the new storyline for the last couple expansioins and the newest (unless I am mistaken, forgive me if i am) that the next race would be a vampire. With Mayong Mistmoore reaching godliness, I would think it feasible that he would be able to create Vampire-kind...just like the other gods created their races.
Without making a new class, I would think the vampire would be able to be a few of the classes...
1. Shadowknight
2. Warrior
3. Monk/Beastlord (bat or werewolf pet)
4. Necromancer
5. Wizard
6. Enchanter
7. Ranger
Natural abilities would be...
1. Hide
2. Sneak
3. Bite ( similiar to the SK's Harmtouch, but it heals the vampire as it dmg's the mob)
4. Lycanthropic ( werewolf form)
5. Doppleganger ( perhaps an exclusive aa that creates a copy, and at higher levels more than one for a duratyion of 15 ticks or until death)
6. Night time only tracking
7. Extremely great night vision
Naturally they would have some kind of dot (sun dot) during the day time.An aa would decrease how much the sun dot lasted and the dmg.
On the opposite hand, I would love to see the new anti-ranger. The vampire would be good, but Im thinking like making a dark elf ranger, but call it a lurker or shadow runner. It would have soome offensive spells/buffs (sow esp.) like a ranger.
They should create better ranged weapons for the classes/races that cannot use a bow. Something like a slingshot perhaps.
Anyway, my thoughts. :-)