Hotkey for the selection of units by rank
I read @Gurken Khan was happy with the solution to use autociv-mod for having a hotkey to select units by rank (see the thread linked below). As I found no corresponding ticket or discussion, I suggest implementing this feature in 0 A.D. main game. Maybe there are more supporters for this suggestion around to establish a proper thread.
In the next step, there could be four buttons implemented for selecting each unit by rank 1, 2, 3 or selecting all (in other words: deselecting by rank). I have an unsued area of the gui between the mini map, the formation and the selection area in mind (see the annotated screenshot attached).