Has anyone tried some of the smaller mbunas with peacock cichlids? I was thinking about maybe Auratus, Kenyi, Labidochromis, etc.
The size of the tank will make a big impact. I wouldn't do it with less than a 55g, but a 75g would be much better. I've done peacock/mbuna mixes quite often. Often coloration seems to have a big impact on aggression. IME, some of the species that I wouldn't do the "mix" with are Ps. lombardoi (kenyii) and 100% M. auratus (should be renamed Melanochromis a..holus). Here's a list of species that tend to be less aggressive that I've either had or currently have housed with peacocks in HEAVILY rocked/PVCed tanks:
Labidochromis caeruleus (yellow lab) and L. sp. "Perlmutt" (bad luck w/ L. sp. "Hongi"
Pseudotropheus saulosi, Ps. hajomaylandia (greberi), Ps. sp. "Acei"
Ps. livinstonii (shell dweller) was housed with sand and almost no rocks.
The vast majority of mbuna will probably grow to be too aggressive for peacocks. People house them together all the time and have success, but people try it alot and end up with dead fish. There is no definite answer just percentages of risk and your willingness to gamble.
FYI, OB peacocks are hybrids that have been crossed with mbuna (as with alot of the garbage OB haps on places like aquabid). That is why they are more aggressive and have little problem, usually, being housed with mbuna.
IME, haps and peacocks mix together much better you just need a BIGGER tank.