All appearance items should be allowed in combat for many reasons.
1.) More money for Anet as I for one will never buy an item I can’t use in combat.
2.) More uniqueness for each character. It will give people a chance to look good all the time instead of being forced to wear an ugly outfit for combat. Some people don’t like the dungeon gear and let’s face it. There is not much choice in outfits with only one or two that even look half way decent.
3.) Will bring in more players who really care about what there character looks like at all times.
4.) Most of us don’t roleplay if you take out tarnished coast server. And if they want to roleplay, give them that option but don’t punish the rest of us.
5.) When you enter combat no one naturally flips into combat gear even if you are roleplaying so that kind of defeats the rp purpose.
These are just some of the reasons to add all outfits to combat. It would really do your game a favor in the long run. It’s only to bad this wasn’t an option to begin with.