Mundane
-berserker e.g. Barbarian
-gunmen/gunslinger (for the steampunk)
-dervish/battle-dancer
-wanderer swordmaster (not really mechanical but...)

Mage
-curse/hex-master/witch
-shadow/dark manipulator
-blood mage
-ritual caster
-time manipulator
-warp mage
-[insert element] specialist
-primorial/ancient magican
-light mage

Rogue-esque
-ninja?
-cat-burglar

(do combo classes like magic swordsman and spell sniper count?)

Wow, total, this list is going to be huge! If the point is openness, you might want to take the opposite approach. Archetypes tend to be really specific after all. Perhaps you should do something extremely open for classes (perhaps reduce to 3 or so basic versions like warrior, rogue, and mage), then support these archetypes with long feat chains (obviously buffing up the number and power of feats). That would likely achieve a high level of customization. Just a thought.