To be able to load an image for the map background (that could be repeated?) This way you could have a stoney / earth background if the game took place underground for instance.
This would also potentially allow for some interesting effects - say for example you had a growing threat slowly covering the map like the approaching fleet in FTL: Faster Than Light. You could show that in the background with incremental image changes (although I grant that it might not work with scale changes).
Regardless, I'd really like to see it for the sake of adding more atmosphere to the screen.
Map background
