I have a friend who sort of has a "free for all, anything goes, survival of the fittest" 120 gallon with pretty much any cichlid in it. tangs, malawis, victorian, centrals, souths, etc.. dont know if he has any chromides in it. anyway at first I was vehemently against this but when I saw the tank in person it looked pretty ballanced and peaceful. the tank was big enough and long enough and had enough hiding places, that the territories were well distributed.
I wouldn't recommend it though from a purely biotopical point of view, it's not natural.