To add a bit more customizability I was thinking there could be class kits.

Basically when you create a character you'd have an option to chose one of its kits. A kit would change very minor things with the class to allow the player to emphasize a specific ability of that class.

Ranger:

Archer:
Archers cannot second and may not wear armor heavier than leather.
When an archer ambushes he must be wielding a bow or crossbow, and it does damage equal to a thief's backstab. Archers may use the ability "called shot" once every five minutes. It increases the chance to hit successfully against the next target.

Assassin:

Bounty Hunter:
Bounty Hunters may not envenom, and backstab as a thief.
Bounty Hunters may "trap" a room. As soon as a mob or perm becomes aggressive towards the Bounty Hunter the trap will trigger and either slow, damage, or poison its target. A Bounty Hunter may also cast track, but not group track.

Rogue:

Duelist:
A Duelist may not second or ambush.
A Duelist has a bonus to dodge, parry, and reposte and also has a bonus to disarm and kick.

Paladin:

Witch Hunter:
A Witch Hunter may not hands or turn and does not know-aura.
A Witch Hunter may cast resist-magic and dispell-magic on himself or allies.