I think competitive PvP guilds struggle to find purpose in a game where campaigns don't have any different rewards for losing or winning. I think BG's don't allow you to challenge specific other players and are 3 sided. I think Duels offer a poor judgement of ability seeing as how specific armor sets and classes can directly counter other ones.
Having a guild war system instanced or otherwise would add a level of competition this game hasn't seen in a long time.
Pride in your tabbard might actually mean something to a pvper again if there was a leaderboard he could look at to see his guilds accomplishment. As it stands now, players have a different toon on every faction for cyro, victory is meaningless.