I disagree, respectfully, I think that the stop-start nature and complex workings of DF would mean that any sort of co-op would severely constrain the game, well at least with respect to fortress mode.
I suppose there could be an argument for taking adventurer mode and making it more like a MUD but I'm not really an AM person.
I would love to play a DF equivalent on a dyson ring. The cooperative elements would be for ring maintenance - keeping the station-keeping thrusters in good health, keeping the trams between territories running, whatever. The balance of the world play could certainly be enough for anyone even dividing the ring up into per-player planet-sized chunks.
I suppose there could be an argument for taking adventurer mode and making it more like a MUD but I'm not really an AM person.