You can already do a shotty version of co-op. Single player maps load into multiplayer using the "open" command and you can play through them untill one of usuall three things happens, you run out of AI or you reach a locked door or you reach some debris that needs to be blown up that can't be.
It wouldn't be overly hard to more of the sp elements into MP but then agian, thats if the person coding knows what their doing.
I'm hoping for some tools of some sort towards the end of this week. It would place LA at their 1 month mark which is when they wanted to release the tools.