Much like Capcom released alternate costume packs for Street Fighter IV, an all-new wardrobe will be downloadable in DLC form for SSFIV.
The first to release will be October 26th. These packs will include new designs as well as original costumes from previous games; no pricing yet.
For some of the new clothing options check out the screenshots below. Capcom has confirmed there to be no plans for Super Street Fighter IV on PC unless they developed some very robust DRM to prevent mass piracy like Street Fighter IV had.