TL;DR
A subtle change that would make map edges more appealing. A "skybox" of sorts.What?
I propose that instead of the very sharp cut-off on the tutorial maps as shown here:
Something like this is implemented:

Not the best example, since using the cliff texture would give the impression that it could be bombed. A different mountain texture could be created for better effect. It could fade out into black as shown in the mock-up or it could be an endless loop of un-walkable looking terrain.