The reason that the don't do the death from space thing, is
Firstly, Mages don't like space, due to the Nearly Dead Magic zone that space is.
Second, Orbiting mages are limited by the surface weather (clouds, Sunflare, etc.)
Additionally, either SR3 Corebook, or Magic in the Shadows says that LOS spells can have their range increased if it is still that character's natural vision. (Binoculars still use your natural eyes. Same for telescopes.)
The only things that can NOT extend your sight range are non-natural sight, such as TV, Security cameras, Matrix video feeds
So I think that it would work very well.
Certainly puts a damper on border crossing over the sea, or sky.
Along the same lines, put mages in blimps, out on the deck and use them Anywhere for the same effect. . .