Trying to play Single Player maps in Multiplayer is not a new idea. It's been tried before. (I remember CyberBlade coming up with the same idea, for example.) A lot of the stuff in SP maps will work in MP.
But not everything will. If there's too much stuff in a SP map that moves, it will cause severe lag for the players and make the map almost unplayable.
Also, cutscenes in SP maps make for a very bizarre experience in MP.