No, bad idea. One of the things I most love about this game is that they don't police in game activities beyond banning outright abuse or cheating. We're all free make deals, break deals, screw people over, or help them out. We're playing a game full of real people who can behave in strange and unpredictable ways. Guild hopping is just another aspect of this. It may be annoying, but no more than getting plundered or sniped. Maybe it should be considered rude, like leveling someone's GB, but it definitly shouldn't be against the rules. Dealing with people working against you is just part of the game. The last thing I'd want is the admins telling me how to play (I mean, besides preventing obvious cheating and the like).