This is suggested every couple of weeks and has been asked to Yoshi P before. His response back then was that they weren't working on it and they would be looking to expand inventory over looking at a wardrobe system.

That was a while ago though so things might have changed. Its worth mentioning though that such systems seem to take a while to create. WoW took about 3-4 years from when they first mentioned they were working on it to actually releasing it.