Nighttime is a majorly important area for Dean, but they need to get the foundation stuff working before deal with nighttime. Power systems, both battery and other, have been discussed and are considerations for the future too… But it does depend on the direction they go with things such as base building and etc… (source).
About the sky, a high resolution texture, even at 4k, will not achieve the current fidelity of the stars. The current stars are actually generated at points using the real location of the star at the maps set lat/lon. So there is not really a skybox at night, just a swarm of vert’s that generate what looks like a star. What they could probably work is making the stars look a bit better (source).