There are a lot of other things that need to be added first, and constellations in general go against the overall feel of SE. It is not impossible that something like this MIGHT be implemented someday, but it would not be anytime soon.

What would be better in the future would be a simple plugin support allowing people to add their own stuff to the engine and sharing it that way, offing most of the unimportant unneeded things to the community.

That's not exactly it. I meant dithering for overall gradient bands on the screen. You can see them on lens flares too.
And in the atmosphere, when you look up the sky from the surface of a planet.

Just came here to say, please please please fix this! Space engine is awesome, but the banding on the atmosphere is so distracting it pretty much ruins the experience

A simple look at work progress thread would answer this request

Better 3D-model of Mimas and new models/textures for Vesta.

If you want to make a better Mimas model that'd be great.

The problem with Vesta is that the Dawn team was not publicly releasing all of their data (unlike most other teams), so we don't have access to enough information to make the appropriate maps. Unless someone wants to make a good 3D model of Vesta and then derive a height map from that model, then there's nothing that can be done about it.

There are actually pretty good models of both Mimas and Vesta (as far as I can see!), but they are made for Celestia.

It would also be cool if when you land on a planet you'd see (depending on the temperature) what kind of liquids are there (water,methane..)

I was also thinking some random events that would occur whilst you would travel through space for example: supernovas, stars getting destroyed by black holes, comets/ asteroids would hit planets etc.