I think addiing a black hole would be both great and scientific.
For ex.,

1. lt will have a strong gravitaional pull.
2. It would consume most of the objects near it with its strong gravitaional pull.
3. And to be more Interstellar-ish and scientific, passing through it will see dimentional changes and what not.
4. It's been proven that a man ages .15 milisecond slower in moon as compared to earth. So by elevating this fact you can do some time changes in some of your far planets for ex. We travelled to a distant planet where the in-game time is 23:40. But in earth (Los Santos), the time is 5-7 times ahead of the former. (I knw this is jst too much, but still).

I knw this a bit of too much but since u guys asked for community's ideas... Here it is. And btw, great job, would love to see the next update and gd luck