Actually, yeah, that would be a good idea for Chun-Li. I can see her being a parallel to Lei (I'm sure most people would say Nina, but just because they're women doesn't automatically mean they're perfect rivals). As for Ryu, that one modded costume I've seen in SFIV with the unshaven face would be interesting. Maybe a traditional outfit like one with hakama or, you know, gi that
isn't ripped?
Guile in an air force dress uniform might be interesting, especially if he had hair that was in military regulation (as strange as it would be to see him without his trademark hair, it always bothered me that fictional characters in the military never have hair that's actually in regulation. I still remember the exact description of it from when I was in JROTC, since we were asked these kinds of questions regularly).
Ken in a suit would be nice, Cammy wearing something that covers her ass would also be interesting. Hell, even
her outfit from Streetwise would be an improvement. Cody (if he's in the game) wearing
his classic Final Fight clothes (without the cuffs) would be easy to do and pretty nice.
A young Sagat would be interesting (hair, no scars, two eyes), although I think that might be better suited as an alternate version (like Slim Bob) than a new skin. In other words, it's not happening.
Adon with his hair down in some way or another would be cool too.
As for pretty much all the other women in the game, it's always nice to see a well-designed costume that isn't just fetish-fuel. Like, casual clothes or a uniform or training outfits make more sense than just slutty halloween costumes.
Oh, and as far as physical appearance goes, I'm sure the Capcom fans will be pleased with the accuracy, since almost every character has official measurements (which I find slightly creepy), as well as a lot of art to reference for the face.