I think it would be great for guilds to be cross faction for current members. Lets say a guild was created on the rep side, you can buy an upgrade to allow cross faction guilding to players that are currently in your guild, but you cant invite players that are on the opposing faction. It would purely be for alt purposes. With the legacy system coming out the incentive to re-roll alts is high and maybe this is a way to get people to play on both sides at a more equal level while still having contact with your main guild, and for those on low population servers you dont have to worry about finding new people to quest with(since it can be a real pain).
Just an idea, idk if its already been discussed?