It'd be cool if you could apply different colours, as well as patterns/fabrics/textures to your Sims clothes. I think that makes sense since this feature will be available in different areas of the game, so I'm quite hopeful for it. Like, we should be able to do it with furniture and different items for the houses.
I think eventually there will be a large CC community, with lots of meshes and stuff to download -- and hopefully if I get my wish, different fabrics, patterns and textures to apply to clothes (and furniture).
Also, I hope CC meshes will still be able to have textures and what not applied to them instead of having lots of recolours.
I don't download much CC, but if there was the possibility of importing your own textures to apply to clothes/furniture I'd totally download them lol. I can see myself becoming quite obsessed.
I think it would be cool if we could change a Sim's hair type too so different styles will look different on each Sim. Kind of like with Pets in Sims 2 - you can select whether their fur is curly, straight, messy-looking etc.