from my best understanding, multiplayer really isn't simply done, and there is much more to add to the game as it is. i really don't see it happening any time soon even if the devs have it planned. it would be super cool getting to watch as a fleet of off-kilter planes attempt to run in formation and accidentally set off their own bombs or something though.

It wont happen. The devs have confirmed that. The only way it will happen is mods. There is a mod in development, but it wasnt going well last time I heard.