Has anyone worked on a "cooperative campaign" style mode?

I'm thinking if you and someone over the LAN/net could have gameplay like the single player mode. At it's simplest, you could have a campaign mode where an ally or more would join you and you could try to beat a level and get credits for the mode. Most complex, two people could play together, or even seperately (say for a head-to-head match against a bot) and then when they meet up later the credits/available levels would update accordingly, and they could play a match again together, with up to 5 friends joining you, one for each bot they would replace.

The enemy teams could be the same, or a seperate menu could "customize" available enemy teams (try beating a godlike team with all player stats at 100).