All that aside for the moment, I've been working up some of the basics of making this a full-fledged 20-level class. Some musings:
Spells Vs. Traps: For the most part, I'm actually opting for spells on this, though I'm considering something akin to the arcane channeling special ability from the duskblade, modified for use with ranged weaponry. Charisma will likely be the governing attribute. Limited progression, 4 levels like the paladin and ranger (I could consider 5 level like the duskblade, but I don't want there to be an insane number of spells per day or anything like that, though having a 5th level would be nice -- if I decide to go beyond 4, I'll most likely look towards the bard spells/day progression instead, but I think that's overpowered with the class features I'm planning). Spell list is something I'm working on at present, but I'm looking at some transmutation, illusion (pretty much solely shadow subschool) and a little evocation for some of the fire-damage traps. What I can't emulate with spells, I think I can emulate with grenadelike splash weapons as best as I can (including the bomb and smoke bomb featured in the DMG).
Hit Dice: I'm leaning towards d8, though I may go d6, depending on what I decide to do for saves.
Saves: Currently considering low Fort, high Reflex and high Will, though I may wind up just sticking with high Will instead.
BAB: Medium, as rogue or scout (+15/+10/+5 at 20th level) -- I don't think the class should be so martially-inclined as to warrant fighter BAB, so I'm sticking with the medium progression.
Skills Per Level: (6 + Int) x 4 at 1st level, 6 + Int each additional level.
Skill List: Balance, Bluff, Climb, Concentration, Craft, Decipher Script*, Disguise, Escape Artist*, Gather Information, Hide, Intimidate, Jump, Knowledge (all skills, taken individually), Listen, Move Silently, Search, Sense Motive, Sleight of Hand, Speak Language*, Spot, Survival, Swim
The skills marked with asterisks, I'm open to removing if necessary -- I thought they might be extra flavor skills. Disable Device was being considered, but I don't know that I want to have trapfinding as an ability, even though it might make sense given some of the "traps" that are being featured.
Armor/Weapons: Light armor, no shields. Simple weapons, plus chakram (I've only got the Arms & Equipment Guide to go on for stats), hand crossbow, kukri, scimitar, short bow (including composite) and short sword.
So far as class abilities go, I'm looking at some bonus feat selections at varying levels, a favored enemy deal (though I'm considering limiting it solely to evil outsiders and undead, in keeping with Diablo 3's setting and background), and the skirmish mechanic. May do uncanny dodge and improved uncanny dodge, but I'm not entirely certain whether I should include evasion or not. May also do a skill mastery for Balance, Jump and Tumble, but not certain there. I'd really like to do something similar to the ranger combat feats, but have it specifically focused on varying ranged weapons, like how the Demon Hunter's Archery skill works -- split it between shortbow, light/heavy crossbow and hand crossbow (I won't lie that I really do still want to emulate the dual-wielding hand crossbows, but the earlier discussion above has me brainstorming there).
My big worry is, of course, overloading the class with a bunch of goodies. That part is going to take me a while to try and sketch out -- the last thing I want to do is have the class be overpowered compared to everything else. I guess we'll see how it goes.