In LOTRO, the character window has an "equipment" tab with all the slots you'd expect for different equipped items, but then also a "cosmetic outfits" tab, which is itself subdivided into multiple "outfit" tabs. The outfit tabs each have slots corresponding to the same equipment types as the equipment tab, and you can put together several outfits you like there. You can then select for either your actual equipment or any of your outfits to be displayed. I really wish SE had gone with a similar slot-based cosmetic system here.

It would have to be a little different here, though. LOTRO doesn't have multi-classing like we do in FFXIV. So where that allows a few outfits per character, this would need outfits for all of our classes/jobs as well as a few extra outfits for some of them. The best way would probably be to incorporate it into our Armoury / Gear Set system, so we could assign both equipment and appearances to each gear set. If you have multiple gear sets with the same chest piece, for instance, but different weapons, you would be able to assign different chest piece appearances to each of them, because we'd be glamouring the gear set itself rather than the equipment.

(In order for such a system to not be vulnerable to players hacking the data to assign appearances they've never earned in-game, SE would need to change gear set data to being stored and therefore controlled on the servers rather than on our client machines, but that's something they really should be doing anyway.)