Before I go into my suggestion, I would like to say that I am aware of the ways in which there are to obtain the different Order Armors and Weapons in game, I just have a couple ideas to make obtaining them more appealing and possibly even throw out a couple ideas for new sets.
From a story standpoint, We are members of either the Order of Whispers, The Durmond Priory, or The Vigil. That is cool up until The Pact is formed. Once that happens, The Player Character is essentially the commander of all three orders. Once Zhaitan is defeated, the least the orders could do is open their shops for the player to get their armor sets. I can understand that there is at least some form of initiation for the orders and that only members of the orders could get their gear. So here is what I propose to make all the sets open to all characters:
1. Create an initiation option that allows the Player Character to gain reputation within the order and grant access to the gear. This is pretty straightforward. Create some form of personal story where players can go and do deeds for the different orders after defeating Zhaitan in order to become honorary members. Perhaps these quests could unlock upon reaching Fort Trinity in story progression as well (since we can already Asura Gate back to the headquarters of the 3 orders). Perhaps it could be a series of quests that when completed it allows the player to have an equipment requisitioner in their home instance for the Order which they have created an alliance with.
2. New Armor sets! Recently, I have been playing Star Trek Online on the side. In their new Romulan content, a Romulan Character must ally themselves with either the Federation or the Klingon Empire. When the player does so, they get new character costume options which are hybrid designs incorporating elements of both the Romulan and either Federation or Klingon armor styles. This idea is a unique way to handle the “You are part of a different order” issue. To this extent, there are many options which I could see developing off this.
2a. Hybrid Order Sets- Armor sets are designed that incorporate aspects of the other order sets. Perhaps a tighter-fitting Durmond Priory Armor with daggers like the Order of Whispers has or something along those lines. This would clearly be a more elaborate approach (OoW/DP, OoW/Vigil, DP/Vigil x3 armor classes), but it could be something as simple as having a badge added to the texture depicting the cross-order nature of the set.
2b. Pact Armor set- In “Forging the Pact”, Trahearne gathers the finest crafters to help outfit the new alliance. We end up getting some fantastic weapon skins at the end, but still are lacking in armor sets. I would think that Pact Armor would be something along the lines of a hybrid of the different order armors. Perhaps a medium set which is not a trenchcoat (or something akin to the old Assassin armors from GW1 would be cool).
I realize that such ideas take a great deal of time to manage and incorporate into the game. Even more, I understand the amount of time new art assets would be to add. I do see the “How does one obtain armor for another order than the one which you selected” question asked a lot. While transmutation is a great way to get stuff, I think that providing a means of obtaining the sets would open the doors to more players using the different sets since they would be easier to obtain. I know new sets is asking for a lot, but I feel that at the very least having access to the current sets would be a great step in a positive direction.