Starsector 0.97a is out! (02/02/24); New blog post: Simulator Enhancements (03/13/24)
That would be less useful than current behavior. Move slowly is not applied instantly. Optimal usage is to activate before the obstacle, when you are just far enough to fully brake before entering it and then disable immediately after exiting.
If you are in hyperspace or an unclaimed system, Go Dark works the same as Move Slowly