A few suggestions of features I'd really like to see and which are not very significant changes:
-Being able to see the gravity force of a planet on the position you are (like for the atmospheric pressure or the temperature:
-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.
-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.
-More speed units: for ships only 3 units exist and they depend of the speed: m/s and km/s (ft/s also but doesn't depend on speed). Why not having km/h and mph as well?
-No more exponent for small numbers such as thousand for atmospheric pressure or gravity. I know this might sound silly but I find it quite inadequate to have exponents for such small numbers, I would rather prefer having thousand or millions like it's done for the amount of stars in galaxies or just a bit more zeros.
-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.
So here's my list of suggestion after spending hundred of hours in SpaceEngine. I really think these small features (except the last one) could make a big difference even though they're not much. I don't how hard it would be to implement those features but I really hope it is possible for SpaceEngineer to include those features in upcoming versions (or even the upcoming one) since they are not much.