While I liked the campaign storyline in mordheim they were linear. I was thinking and hoping that there would be a branching set of stories for the houses in necromunda.

One possible idea I had was that at certain stages the mission giver would say that you need to get a certain set of objectives completed before the next story mission unlocks. For instance:
Quest Giver: "I've got a really good opportunity for you to earn more credits than you've ever dreamed of, but my employer needs a gang with a certain set of skills. I want that gang to be you, but you ain't good enough yet."
To be able to unlock the mission you'd need to fulfill a set of objectives by fighting in random campaign games. Maybe you need to make a kill or raise your gang rating by a certain amount ect...

Also I was thinking that at certain points you're given a choice between two options, number one could be a known level of gang to fight or you could gamble for a random gang, however the gamble means possibly less credits if your opponent is weaker or a harder fight if the gang is higher.