The electricity system is really disappointing as it stands now, my space station has many solar arrays and a fuckton of batteries, but i have no use for it. Still waiting for electrically powered motoric stuff like pistons, rotation motors with like 4 nodes (1 in each direction) where you could add the stuff that you need to rotate, these 2 parts combined would allow us to make fully controllable robotic arms to make for example rocket assembly stations in orbit.
Also, the capsules and probes should use electricity, after all the probe theoretically constantly sends and recieves data, so it should have by itself an electricity usage of like 0.25-0.5/s, and the capsule maybe 0.5-1/s because it contains systems that the astronauts need to survive
Just an idea, but i think it would add as well to realism as well as to the challenge if you had to have electricity storage and generation on your rocket as a mandatory requirement