I think it would be neat to have a multi-tiered guild system too, like instead of a straight up ladder there could be multiple branches that are equal which members could join or be elected into/through. The whole hostile takeover concept could also be cool, if guilds could have their own internal revolutions.

Imagine the potential, it could open up whole new ways of playing the game. There could be an in game revolution spanning multiple guilds, it would introduce real subterfuge and conspiracy, it would make having stealthy spies handy a legit part of the gameplay.

And if there were different kinds of guilds, things could get really interesting in terms of guild politics.

For some reason, in most MMO's, the structure and politics of guilds get the least amount of attention and that's tragic because how the guild system works can have a huge impact on the game, after ask anyone playing an MMO the number one reason they stick around and usually their Guild is one of the first things they mention.