It would be cool to have a toggle to turn on a ship path display on the sector view like this:
In this example:
Green/Purple is a round trip trade ship.
Red is a one-way trip by a combat ship.
Blue is a one-way trip by a probe.
Yellow is a one-way trip by a colony/mining ship.
I imagine these to be like an ant trail, with the arrows moving down the line. I also imagine them to have a ~35% base opacity and the number of ships that are currently taking that path would increase the opacity up to 100% as the number of ships on that path gets closer to 10 or whatever. Maybe the opacity scaling is different for different types of ships. You can see that the opacity of some of the trade routes is different, which is meant to represent that some trade routes are more heavily traveled than others. Also notice that along the yellow trail there is a very slight red trail as well, to represent that there is a small defensive fleet accompanying the new colony ship.
I didn't put this in, but perhaps trade routes that are intra-system could be represented by a green and purple circle around the system on the sector map? I don't know.
This could also show up inside the system view to show paths between planets.
In general, I think that this would make it pretty clear what the major routes of your empire are from a glance, and where you'd need to be spending most of your resources defending those lines.
Furthermore, there could be technology that would allow you to display enemy AI routes from a distance and then additional technology to block it and reveal enemy detectors. New ranks could expand the detection radius of your colonies? Or perhaps it's a ship itself that does the detection. Knowing enemy trade routes could really make for really interesting piracy game-play or general hit-and-run tactics. I imagine that the detection could be deepish science, which would give the science tree some more combat applicability.