This would be taking the Refit Simulation a bit further. But, I think we can do better than this. How about an Instant Action mode, that would double as this suggestion but also allow you to build two fleets (or import presets) and have them go at each other? You could customize everything; objective layout, astroid level, AI intelligence, and so on. You would be able to refit any ship you like.
Presets would govern general battle setup, like "Large Fleet battle" or "Strike Force v. Capital Ship." Like missions, only more customizable, and sans backstory.
I was going to make a post about this, suppose I might later.