PVP Guilds

Blizzard is apparently creating a parallel mini-guild structure in the expansion for pvp arena teams. I think it would be great to go even further in a game and establish several other parallel guild structures. Friends lists are a simple and common example. But also, a guild structure for crafters/merchants (cartels?). A guild structure for pvp teams in general (armies?). Etc. People need to have more than just one social circle in a game and the game needs to support that.