There is at least a possibility that there may be some kind of multiplayer support eventually.
From the old topic News from the front
Regarding mods - It's really a question of where we put our effort in. Right now it's in the game and not in providing a mod toolkit, though obviously we have a whole range of tools to make the game. It would take some effort to make them usable for the community, but if the opportunity would arise, it'd be something I'd very much like to do. I guess it'll really depend on how much demand there is for such a toolkit. I think it might be more sensible to link a mod toolkit with a multiplayer mode, than just release it for single player.