I'm new to this forum. First of all, let me congratulate the author and contributors for this wonderful simulator. I believe it is the best I worked with, and I did work with a few.
As for my suggestion. I feel this might be quite heavy, but, as a personal curiosity, I always wanted to see the relativistic effect of light speed in such a simulator. That is, when aiming for a region in deep space and travelling at speeds >c, you could actually see the galaxies shifting to new positions, closer and closer to their real position, until near them. Of course, that would work also for the galaxies left behind as you would start seeing them shift as well based on the light at current position.
As said, I believe this to be heavy as nearly every object would need to implement a path and also, such an implementation would open a door to organic formations, such as the birth of a star or the end of it.
It would be nice to travel at high speed from a recently collapsed star and see it's destruction in reverse.
However, as I don't expect to be a realistic feature to implement, at least, what do you think about it?