I think another expansion is a must. Develop a lore a bit more, add some additional features (Quasi Space, Below Space (even if these are just additional @layers@ of the main hyperspace (sector) map) etc.), more assets across the whole board (stars, planet types and planet visuals (where are the ringed planets????, comets??, black holes), ruins, stations, ships, modules, aliens, critters, even mineral types), tweak the tools a bit. You can still start your work on the sequel in the meantime:)
I think there must be some form of contest for the modders, writers, visual artists, composers, even voice actors. The best story mod, best ship, best new module, best art, game tune etc. More attention shall be drawn to various mods. I am sure that many will be ready to surrender and waive any claims to proceeds if their assets of any form get included in the official game
Any licensed universes around? babylon 5, star wars, halo, warhammer 40k, star trek, mass effect, Lexx, Wing Commander, GalCiv, BattleTech, X-Com, Age of Wonders Planetfall, Sins of the Solar Empire, Known Space, Starflight etc.? Any total conversions? A remake of SC2 (yeah-yeah - legal issues...)?