I was actually coming up with some vague "campaign Point" rules for the campaign.
Basically, whenever a faction (Corporation or DL faction) wins a scenario, they get a certain number of points that can be spent on future scenarios, for things like buying Barbed wire so it doesn't need to come out of your build point total, to limited contol over a scenario, reinforcements, etc. I figure with enough points, you can shift allegiences between factions, so you could build your army from different Corporations or somesuch.
(example: Capitol wins enough scenarios to be able to "buy" an alliance with Mishima. For the next few scenarios, Capitol forces [regardless of player] can take Mishima units in their army build)
I figure this, combined with the narrative connection between scenarios, would make for some interesting strategies.