i prefer the idea of dark-light channels rather than guild-alliance channels as those easily become redundant imho...
kohaku san, would creating another chat channel (other than @main) require a server recompile? (i really have no idea)
if it didn't, perhaps a script could be attached to it to identify alliances (there must be an identifier for that as the allegiance NPC attests to it being there) thus banning dark siders from the light channel and vice versa...