I think that the a planet style esque combat system, and a rgp element with skill points, and destriod/valkyrie skills, would be cool, and being able to socialize would be cool, and mayb, here are some ideas I have
Maybe falling in love with someone could get you some kind of bonus, like stamina/or health, but to stop people for joining relationships with other people quickly, the longer you stay in the relationship the higher the bonus is, with some sim esque system of managing it,
If you could pilot destroids, you should have something to do, example: small wave comes in, and all the valks nuke 'em before you can even get a target, so maybe they intorduce some kind of landing craft that land on sdf, and initiate combat with destroids
and a pen and paper rpg would kinda be cool too