: Alternatively, would
: this require the presence of the (disabled) Marathon application?
The Aleph One development build does indeed use the Marathon application for its resources, just as it uses Shapes, Map, etc. Along with the terminal text, a few key images are in the application's resource fork.
None of this has to do with co-op, however: exploration missions are the problem. As you may already know, Marathon's exploration missions require you to look at the "must-be-explored" polygons so they show up on your automap. In multi-player games, the automaps aren't shared between players, so player A doesn't know which goals player B has visited. This makes it impossible to sync up the "did we complete the mission" data, so your co-op game would almost certainly go out of sync on the first exploration level.
Marathon 2 changed exploration missions so that you have to stand on the goal polygons; this is information that is shared in multi-player, and co-op is why they changed how exploration works. Until we work out a substitute behavior for Marathon 1, we've disabled co-op so you don't run into a game-ending OOS.
President People does get an honorable mention for his guess. If we get that far, terminals in co-op games will work like M2 and not pause the world. Right now, terminals don't pause the world even in single player, and the engine is being stubborn about it too. Every time I stop the AI and game clock, the game stops listening to my key commands, hanging the entire engine.
