Lol, I'm getting excited for multiplayer and I haven't even played this game yet. I temporarily don't have access to a computer that belongs to me, or I'd totally would have downloaded this and started designing stuff.
One question: when you guys talk about multiplayer, are you imagining a bunch of people on the same server just doing whatever, or a more formal game (aka, explicit teams, rules, efforts to make both sides start with the same resources?).
Cause if you want to go with a formal game, I've come up with an idea: there are two teams, each of which has a single ship designated as the "nomad". Each team starts with one of those nuclear reactor things and a box of resources (the same for each team), and everything they build on top of the reactor counts as part of the nomad. Each team has a point in space (probably marked somehow) that both teams know about, that their nomad must return to at various intervals. If your nomad's reactor is destroyed or it fails to get back to the target point in time, your team loses unless they can prevent the enemy nomad from reaching its objective in time, in which the game is a tie. Otherwise, anything goes: mining, building whatever, boarding, guarding the target point. The idea is both teams can do whatever they want, but they need to stay in the same area and the one team can force a fight if they feel they have an advantage.
...Does that make any sense? I know I just designed a game mode for a game I haven't played, but I was too excited not to share. Feel free to say if its not a good idea, I could go on about the details if you guys are interested though.