From what I've seen so far, I'm really not a fan of the alternate costumes (including those that you stupidly had to pay for as DLC in regular SFIV). 
  
If you had the power, what sort of costume styles would you have for the SSFIV cast? These can be vague 'themes' or existing costumes carried over. 
  
I wouldn't mind seeing Chun Li's Alpha costume. It was probably the first time Capcom actually bothered to make alternate costume sprites (as opposed to SNK who frequently made new sprite sets for existing characters).
 
Ryu needs his silly red SF1 slippers back. 
 
It would make sense to have Copy's FF costume- although it'll obviously already be in the game.

I'm sure some of this has been done through PC version mods.

An Ibuki outfit where she's still in her civvy clothes, so she'd smoke bomb to change, but was still in the same getup.  Then again I don't think she has that opening animation so maybe not :P
 
Perhaps secondary outfits that are seen in the Street Fighter Legends comics? I guess they're generally in their standard clothes anyway, but it would be good cross promotion.

All mecha versions of everyone.

I just want Chuns alpha costume. Maybe Ryu with regular clothing
 
Sagat looking like Bob Sagat would be cool too

Drag, I was hoping this was going to be a discussion about Halloween costumes. 

" Drag, I was hoping this was going to be a discussion about Halloween costumes.  "

Nude costume of Juri, Chun-Li, Cammy and Hakan...  What?
 
I'd say each character have a tuxedo variant.  Make it classy!

I'd like to give Dhalsim a Richard Simmons-esque workout suit.

" All mecha versions of everyone. "

Ken in a thong sporting one of them fancy beer caps. Reminds me of myself on drinking nights.

Any of the "alternate" costumes that the fighters may have worn in other games.  This means Chun's Alpha outfit, Ken's Alpha long hair/pony-tail with ribbon combo etc.  Beyond that, I'd just like costumes that actually make sense for the character.  They got a few of them right in the first game, but all the ones they added beyond that seem to be... not... good.

Ken in a brokeback mountaaaaaaaa.....aannnd never mind

Where is Seth's business suit! It's the only logical alt costume they should have put in for him! 
Instead we get pants and weird glowing things coming out of his joints.

" Where is Seth's business suit! It's the only logical alt costume they should have put in for him!  Instead we get pants and weird glowing things coming out of his joints. "

" Ken in a thong sporting one of them fancy beer caps. Reminds me of myself on drinking nights. "

" @Satune said:

" Where is Seth's business suit! It's the only logical alt costume they should have put in for him!  Instead we get pants and weird glowing things coming out of his joints. "

Where's the Seth costume where it's just replaced with Abel's model? "

" @jbrader said:

" Drag, I was hoping this was going to be a discussion about Halloween costumes.  "

It can be if it's about SSFVI characters wearing something special for Halloween...  :P "

" @lordofultima: Good catch. Sometimes I get so excited about Halloween that I start transposing roman numerals. Now all of Giant Bomb knows my secret shame.  "

I'd like to see some Darkstalker's homages.
 
While not exactly one, Rufus's costume is very similar to Hsien-Ko's

Fei Long alt costume dressed as Yun/Yang clearly. They're already in Chun Li's intro...

" @jbrader said:

" @lordofultima: Good catch. Sometimes I get so excited about Halloween that I start transposing roman numerals. Now all of Giant Bomb knows my secret shame.  "

What the F*** does Transpose mean!!!!??  LOL!! "