Hey, nice! I had a classic idea pretty much like this, as well. Tried expressing the idea to others years ago but it didn't go over so well.

Vana'diel Vanity has a certain ring to it.~

In a world where only select few equipment choices are accepted as "the norm", there sure isn't much room for fashionable diversity. Ever wanted to tank in wedding garb, swimsuits and other such event wear? Wear a full AF/Relic set without being called a gimp, freedom to choose exactly what you wanna look like for others? Well, if only stuff like this existed..!

By registering equipment to vanity slots you'd be able to change your appearance without altering your statistics. The only requisites? You need to be able to actually equip the "vanity" gear according to your job/level. The vanity slots might be too difficult to create a new menu or equipment tab for, so why not let an NPC (such as your own personal moogle) handle it? Can it really be that difficult~?

The best part? Wearing vanity equipment would allow you to always appear as such no matter what, even if your "real" equipment is swapped around, your appearance will stay the same until you specifically change your vanity set . A solution to the ever-present "blinking" issue as well!~

The only complicated snag, I feel, is what to do with weapons. I think maybe they wouldn't get vanity slots. It just wouldn't work. Wouldn't be much of an obstacle anyway - as front-line jobs don't change their weapons all that often. While back-line jobs do change weapons often, they generally need less cures and support than front-liners tend to, usually. Thus, weapons would remain as-is and you'd still blink when swapping them around.

It'd be really nice to have this, I feel.