I know what you're suggesting, but I really don't want to do this.
For a start, the game is a campaign file, which means that it can't be played multiplayer to begin with. The maps would have to be separated out. Except this won't work, because the maps would be larger than 8 MB, and multiplayer maps have to be under 8MB. The only way to get them small enough would be to remove the music, which I don't want to do because I feel the music is very important to making the campaign what it is.
Plus changing the maps in this way isn't a small job - there's a lot of thing related to the balance, abilities, and triggering that only works in single player at the moment. I'd have to re-do almost the entire campaign (which took me 6 years to make) to make it multiplayer.
I am considering one last big new feature for the campaign (voice acting) but I'm not keen on making what was designed as a single-player campaign a multiplayer one because of the sheer amount of work that would be involved.