I think it could clutter up the map. Also as tanks are not that maneuverable, it's often pretty easy to guess were they are, with spawn so close to enemy or friendly bases. 1 mile doesn't matter much when you are in a plane trying to cover them.
Also, when trying to precisely locate a friendly GV in range, hit shift-F4 for a moment - their icons will show up at exactly the same long distance as any friendly plane icons.