I like the idea, but I worry it would basically become pretty much as effective as an advanced radar for most uses, for less cost. I mean, even if the sector is very narrow, all you'd really need to do is sweep it across the front line depending on where you need to look at the moment. It's now adding micro but probably not a great deal of fun, for the cost saving of maybe a single mid-sized unit.
There aren't that many times when you need more radar coverage over in your side of the map once you've established a front line. Occasionally, yes, and in those times an advanced radar that hasn't been killed yet will fill in those holes - but a couple of standard radars could also do that.
If we're going to do something as an additional information structure, I think I'd prefer a telescope. Build it somewhere, select a single point it can reach in line of sight, and it will then provide a vision radius around that point. Ideally, this should also indicate to the opponent that this area is now visually observed.
I would imagine the easiest way to do this is have the telescope be able to once-off construct a unit (like the Djinn lamp) which is untargetable and has no physical presence, but is still visible to the opponent and grants vision in a radius.
If necesary, some sort of check could be done every few seconds to see if the original telescope still has no terrain interrupting its line of sight to the vision point, and if it does, the vision point... changes colour and stops providing sight? Stays around until the telescope itself is destroyed, though, in case the land is terraformed back down or whatever.
This would be an excellent anti-defense structure as it enables better information and targetting of fixed defenses, but it's quite counterable as you know it's happening (justify as lens glint or optical tracking or whatever, it's high tech!).
I would imagine it might have some uses in monitoring an otherwise undefended area too, in case radar-jammed things are trying to sneak through. Cloakers still defeat it obviously, which is fine.
