Is it planned to be able to record executable scripts at a fixed frame rate? I think this would be a nice way to make videos of space engine with every frame 100% loaded and high quality.
Yes, this is already works.
-Possibility of moons having moons since it's theoretically possible if the object is in the Hill Sphere of the moon and far enough from the planet they are orbiting. I know Elite Dangerous has this type of configuration and it looks very cool and still is realistic.
You're wrong, moons of moons are not theoretically possible. Even for lightweight planet and very far moon, like our Earth's Moon, its satellite could exist just few years.
-A simple thing which has always been something a bit bothering; prograde/retrograde etc. manoeuvres are always rotating the ship in a certain position BEFORE orienting the ship in the right direction which makes the manoeuvre slower and can disorient when not looking at the ship (in orbit camera f.e.). This simple change would certainly make a difference for people using ships because it becomes quite boring after a while.
I really don't understand that you are asking.
-Lastly, the biggest suggestion I have: a fuel unit (in gallons/liters) telling you how much fuel you have consumed since your ship has spawned. This could give a primitive gameplay element leading to some roleplay travels during which a certain amount must not be exceeded. To go even further, maybe being able to set this limit in-game making, as a consequence, when exceeded, engines useless.
Fuel system is a large work, not has been started yet.