A few ideas for discussion:
I think it would be great if there were ways to customize clothing as easily as one can customize bodies. In particular, I think it would be a great feature if there were a base t-shirt and you could select or set a color and choose an image graphic file and get a t-shirt in that color cloth and with the graphic incorporated. T-shirts are very common clothing worldwide and one could quickly produce a wide variety of different T-shirts for scenes with several characters with minimal effort and without requiring the skills that are necessary to produce clothing with MakeClothes. This would greatly increase the amount of customization that a beginner user could quickly and easily accomplish. If one wanted to go all out one could produce a few versions of the t-shirt suitable for different types of poses and/or with different wrinkle patterns or that hang differently (e.g. very tight or over-sized) to add variety and avoid having multiple characters with identical winkles in their shirts.
Right now there is a huge gulf between ease of producing a customized body and producing customized clothing, I think this would narrow that gap somewhat. Perhaps that's a plugin, perhaps it's a standalone MakeTShirt program.
Along similar lines, a while back Joel posted a thread about some textures that Pixar has made available that included one of the female outfits with several alternative textures. I think it would great to have a newbie-friendly way for people to customize clothing with different textures. By newbie-friendly I specifically mean without having to use Blender. If one could easily pick a different color for a suit, select pinstripes, make it a tweed jacket, change the pattern on the dress shirt under the jacket, change the pattern on the tie. etc. I think it would have a lot of flexibility and appeal. I'm guessing that some or even all of this can be done using the material editor, but even if it can it would be nice to have a more newbie-friendly interface.
Lastly, and I am least sure of how useful/how much of an improvement this would be, would be a MakeTarget for clothing where I could load a character with a pair of pants and a shirt and tweak the shirt to work with the pants. Maybe this is already possible with MakeClothes and I just haven't seen it. Right now most of the available clothing comes in fixed ensembles rather than individual items that can be mixed and matched. I presume this is at least partly because of the difficulty of making separately, for example, pants and shirts that interact nicely with one another.
Like I said, these are just brainstorming ideas for discussion.