Think of the lag if an Imperial Guard guild and an Ork guild go to war.
It'll be nonexistent, due to everyone being a space marine.
I actually think a necromunda MMO would be FUCKING FANTASTIC.
Just think, you and your mates form a gang, start carving out your territory in the underhive one bloody inch at a time. Its got everything, trading posts, betrayal, an overarching set of factions in the gang houses... Rare archaeotech etc, hired gun classes for people who don't have friends (sorry, 'like to solo' i think the term is, i'm sure theres a masturbation joke in there somewhere)
If your gang gets too good, maybe they set the i'llbeatraitors on your ass, or worse, maybe you and your mates attract the attention of a group of spyrers....
Basic encounters with ripperjacks and rats as a juve. Expansion packs add more areas to the underhive, new gangs too, like ratskins etc.
Its perfect. Shame it'll never get made.