One feature that would be an install sell for me is being able to program my crafts, I already used the Kerbal OS mod for KSP but it is somewhat clunky.
Features that would also enhance this would be being able to set a fixed timestep and then simulate it as fast as the computer can and also a headless mode.
They are considering this, I think it was suggested multiple times. For now you can make quite complex stuff tinkering with xml by adding activators and binding input controllers like this 7 segments display
The game as it is right now is already an instant sell (and relatively cheap!), but you have to think that this is going to have heavily customization for engines, a planet builder and I have high hopes for the career mode. If you have the money and are thinking on buying it I would suggest you to do so :)