As the title would suggest, i think it would be pretty sick to see something for cosmetic item sets for players to set outfits and such!
It's one I brought up a few years ago and I believe Teddi and Killermon were interested, I think it's more the logistical issues. I guess they'd have to store those sets somewhere for each unique player, and recall them in a timely manner when called. When a game like WoW added sets it was significant but they had the mechanics for it I suppose. Overall I think it'd be great to save a few sets and would encourage a much wider use of the many items offered in the store, as changing an entire set to something then back is pretty laborious when done one item at a time.
It's always been on my list of things I wanted to add. Unfortunately, it's always fallen into that camp of being a lot of effort to implement versus the amount of people that would use it. Most of the effort would be in the GUI for it, and making it intuitive and not clunky would take a quit a bit of time. One day, maybe, but the time spent implementing something like this is probably better spent else ware on features that would affect more players.