So, there is our development plan. 
The plan is not fully correct and it can be changed, but for now it describes the priorities of various features, from highest to lowest. 

  • Save Load
  • Non-rectangular modules which allows to build more interesting designs
  • Multiplayer
  • Production, Salvaging, Ammo
  • Warp drive, tractor beam, energy shields, torpedos, harpoons
  • Crew
  • Advanced AI
  • Trade
  • Random generated missions
  • Resource extraction from planets

Also, bugfixes and various minor improvements have a maximum priority in most cases.