Replays

[CodeFantastic]

 I'd love if you could launch a rocket into orbit and carry out your mission, then replay the events without the GUI and worrying if your rocket is still prograde. 

Of course, it would only last up to when you go back to the space center, but it could also help with troubleshooting problems with your rocket/plane without redoing the mission several times.

[Mr. Scruffy]

An in game record and replay function is a great idea. You know like in World of Tanks or in racing games.