Although most suggestions here go unanswered and unnoticed, this one should really be considered. I really don't see a downside by making everything tradeable. Pvp players can safely earn extra income and non pvp players can grind to buy something that is locked behind pvp coins.
I forget which event, but the time when a new items were released daily and only available for 24 hours to purchase was amazing. Even something like that for pvp cosmetics would be great if not tradeable 24/7.
I'm sure this will be ignored just as almost all other posts but hey +1 for what it's worth