I rather like that idea as well. Although rather then builders, why don't we have the scout star ships deploy into them like a colony ship does?
Probably to avoid being able to just plant one of these on any planet you can reach with a scout.
Although there's a valid question of whether that would actually be a problem or not. Once you've got a scout on a planet and cloaked in a corner somewhere, they are effectively safe there for the rest of the game.
I don't see why any scout unit couldn't have a one shot ability that destroys the scout but drops a cloaked 'scouting beacon' or some such thing. Although really in that case all we're asking for is a higher cap of scouts in order to be able to picket every planet in the galaxy. So then the question really is whether scout caps are some finely balanced game mechanic, or just a number that was tossed in because hey why not? I assume it's not intentionally balanced around anything, since changing the number of systems in your galaxy doesn't change your scout caps either direction. So a 40 planet game you can easily picket every planet, but a 120 planet game it's numerically impossible to do so. I don't think it really throws off the balance either way to allow higher scout caps or to allow scouts to turn into immobile beacons and free up cap space. But I could be overlooking something?
Now that we've thoroughly hijacked and derailed this topic, discussion can begin.