I apologize if I've already said this on your Civ V mods.
I think a good addition (if possible; I'm not a coder) would be one which would allow explorers to act as artillery spotters for ranges units. This could be fan-wanked to be that when an explorer is adjacent to the ranged unit, it represents the communications section while the real unit is behind enemy lines. This would give a +1 range bonus to the unit and make explorers more useful.
For a space game, Civ:BE blows when it comes to tech you'd expect. I mean there are no space elevators! You should be able to build a few. You should be able to build projects which would send a probe to an asteroid, which would deploy robots to starting working on it and moving it into orbit. Sure this would take lots of turns but later in the game you could get a *lot* of production bonuses and possibly things like titanium.
Also, I think the anti-satellite combat needs reworking. It's too easy to shoot them down. I mean really? Ground based artillery shooting down things in orbit? Did anyone in Firaxis realize how hard that would be? I mean the range implied is a LOT more than the hexes on the planet.
Any chance of porting over the Civ V mod of having cities on ocean tiles? I think they should have a population cap but still, floating cities are a common sci-fi component in a lot of books, especially those by Kim Stanley Robinson.