Credit to @Random for his Map options for alliances idea. Specifically:
Tagging enemies and allies would be very useful, but there are uses beyond the map too, and this could replace the current bookmark functionality with something far more useful.
We can start with players, and then families, but eventually we should be able to tag planets and systems too. That way you could, for example, tag a planet or system to always watch regardless of who owns it, and in a list view as well as the map view.