I think this would be really neat. I dont know about having them on cloaks or breastplates, too complicated/gaudy, but i could see forming up a raid or an event and give the raid leader the option to name a standard bearer and have a flag on a pole with the guild designed emblem on it during your raid. Or maybe temporarily planting it in the ground until the raid disbands. Imagine riding up on another guild raiding an overland target. Whats going on? Who is that? Oh, it's guild soandso's battle flag! just my thoughts on it :)