You remember that problem when the fortress is besieged and the enemie has a strong splash (Collosus, Infestor,..), your army get massive dmg because each enemie unit damages all your units.
Also it would be nice to be able to control the startpositioning of your units, eg. zealots in front, archons behind, immortals behind archons..
This would add some nice more strategy to the game.
Solution: Order the units near the fortress on a field, using the same positioning the buildings have on your building island. After opening middle, that second side could be placed behind the fortress, as then usually more higher level units are build.
Visual gimmick: Use warp gate animation for protoss units.
Also the enemie army should stop attacking the base if they can attack units as soon as they are spawned (I don't know how difficult that AI change is).