This interests me, because I'm now getting a better picture of how writing broad rules for a system differs from writing specific crunch for a setting. Probably obvious to many, but I'm slow that way...
I really do like the idea of a character that's built of component Abilities, Perks, and Sperks. I hear you on the GURPS model, and Savage Worlds does a good job of "classless" characters, too. From a game balance perspective, I think it can be done as long as characters pay for what they get (in terms of AdCost). The "label" of class does impact Sperk choice and some advancement details, but nothing one couldn't work around.
So (just thinking out loud, while typing) you might say here's a group of humans, let's call them Cimmerians, and they live in this cold, hilly place. OK, that's your race, so you have some base stats, some Perks, and a few Sperks to choose from. Now, instead of saying, "Pick a class," you follow the class-less method above, which is totally in-line with the Chimera rules, because the AdCost values are the same.
But when it comes to Sperks, you consult your custom Sperks table - base it on region, or archetype/character vision, or maybe even social background (?). Maybe they're good at backstab, but don't necessarily have to be a "thief." Maybe you could get a power-school Sperk, and just say, "Yeah, my character apprenticed with some sorcerer." Difference here is that the Sperks are justified by the character's role in the setting, not the class as defined by the system.
Anyway, I see how this could work, and now that I'm thinking on it, one could mix-and-match the Sperk lists in any combination desired. This actually fits in very well with the describe-a-setting-through-game-mechanics mantra I've been on about lately.
Thanks much for this, October - please keep me (us) posted!
-Erin