The only problem I can see is with diet. One or both are going to suffer.
Rusties being Herbivores and Peacocks being Omnivores it might be hard to feed the proper diet
to both. New Life Spectrum appears to limit this problem but I am still a bit sceptical.
Diet wouldn't be my first concern. I have about 20 rustles (supposed to be peaceful) in with maingano (supposed to be pretty aggressive) and I can tell you that some of the rustles are considerably more aggressive. The alpha male aims most of his aggression to the submales but some of the larger females can be really nasty to the maingano. Nothing serious but you'd expect it to be the other way around. I would look into slightly more aggressive peacocks just for a little extra peace of mind.
I have a few labs and zebra (all male so no threat of interbreed) which are omnivores in there too and a healthy diet of mainly greens and then some meat flakes every 3 days keeps everyone happy with no signs of bloat.
Well I am keeping a 55 gallon I want 4 rusties and probably 4 peacocks....I read in the Lake Malawi Pet guide that Rusties were non aggressive.......smh I want to mix the tank with mbuna and peacocks how can I do that?