I never expected I'd get hooked on a game that is far from being complete. The ability to build my own spaceships gives me an itch No Man's Sky doesn't quite provide with its corvettes, even if here thus far I've only managed to build a cramped rocket-van that I've then recycled to make a somewhat roomier shuttle resembling something from Space: 1999.
The controls are fine for me (except for the lack of pausing), but it'd still be decent to provide customizable key bindings. And an ability to crouch! There was that one time I needed to refuel thrusters but couldn't reach them because I installed them in an alcove close to the floor. An ability to install thrusters on the surfaces' away side would also help immensely with bottom thrusters.
Trying to move around early on --when you have to pull a lever to turn thruster on, rush to the steering wheel, then rush to the lever to turn thruster off-- is annoying (perhaps there could be wheels for making planetside vehicles?), but getting into orbit and watching the planet spin below you, secure that you won't fall any time soon... that is immensely satisfying (even if there seems to be a physics trick that synchronises your spacecraft's speed with asteroid's).
There definitely should be lights players could install to provide lighting inside vehicles or to make them visible at night. About the only way I could see my spaceship at distance in the dark is through all the red cables visible through its windows, and having only weak aqua-colour lights to provide light inside isn't pleasant either. I'd even suggest audio beacons producing regular signals to help locate one's ship.
Iron deposits could also stand to be more plentiful (whether that's being more common or providing bigger yields) when you need so much iron to build a decently-sized vehicle.
It'd also be helpful to have doors to close when you pass through them. Would make returning from EVAs less of a hassle.