Hello! :)
A multiplayer mode in Starsector is a great idea and we all would love to see it, including the developers of the game! Unfortunately it is not something that is going to happen. Fractal Softworks is a small developer team with limited capacities. They decided to focus all their energy on the single-player aspect of the game to make it as good as possible. By now there are many technical and game design barriers, too. If you want to know more you can read the
FAQ on the Starsector homepage.
So, there's no chance, sorry. Don't let that demotivate you though, come up with other new ideas :)
As a general advice: It is a good idea to use the search function (upper right corner) to see if anyone posted a similar suggestion before ;)