The Idea to break it. If that makes sense

[Mekose]

Well, Amnesia and it's engine is set up and scripted to be a solely single player. Adding a new player would really fuck up the script, so I doubt it would be plausible without a ton of work. Even then, it would be easier to make a total conversion in source or another engine. I doubt it will ever happen, same thing with Oblivion Co-op. But then again, I can't speak for Frictional, they might be able to add multiplayer with enough engine edits.