Looks like the multiplayer coop campaign mode present in the XBOX version has now been comfirmed in the PC version as well.

We had some very ambitous designs for the multiplayer, and we did not advertise on the exact content until we were sure to be able to deliver it. Things such as simulating a fully interactive physical environment over the network were risky, but we are now comforted that the cooperative mode will deliver unprecedented experience of multiplayer gameplay. The domination mode is also very promising as it changes the control of areas to something more interesting than simply capturing flags. More info to come soon.