I'm not serious about this idea since I'm a bit preocupied with other things, but what do you think about this idea:
A space combat sim with LEGO ships from 1979 to 1998. Basically, Classic Space, Space Police I & II, Blacktron I & II, Exploriens, Ice Planet, UFOs, Insectoids, M-Tron, Unitron, Spyrius and Futuron (Roboforce doesn't have proper ships of their own), all flying around and blasting the crap out of each other. It doesn't even have to be combat - the game could also have peaceful exploration, mining and trading. Of course, not to nearly the same degree as Star Citizen, but perhaps on the level of Evochron Mercenary? You could even build your own ship LDD style, using bricks and elements from all the above themes (including Roboforce this time) - but you'll have to unlock bricks by buying the ship kits in a shipyard or broken-down ships in a "brickyard" first.
As for a storyline, well, does it really need one beyond "Blacktron hates everyone, Space Police keep the peace, Ice Planet and Exploriens are rivals in exploration, M-Tron is obsessed with magnets to the point of trying to steal everyone else's, the Insectoids are just there, the UFOs are just now probing this area of space, and everyone else has no point except to give you more ship designs and more things to shoot at or trade with depending on your faction"? Of course, it obviously wouldn't take itself seriously.
Again, though, I can't stress the fact that I'm just dumping the result of 5 minutes of brainstorming while reading Legostar Galactica here and am not planning on taking this idea further (though if anyone else wants to you have my permission - it's not really that original of an idea, after all, since it's just basically throwing LEGO at the space sim genre and seeing what sticks). Also, if you have any ideas to add, go ahead.