potent pawn
What are you thinking about sub-group units?
This would add the possibility, within a group of different unit types defined as "1," to select only long-range weapons or any personalized units within that group.
For example, in a group of A, B, and C units:
10 A
5 B
30 C
(Existing) To create the group, use Ctrl+1 after selecting all A, B, and C units.
(New) To create a sub-group, use Ctrl+1+1 after selecting "1," then select only 5 B.
To select the sub-group, select "1" then "1".
dense warren
Not exactly what you are asking, but you can sort of do similar things with custom keybinds.
E.g. this line in uikeys.txt I think selects non-aircraft units with weapon range less than 470 near your mouse cursor. I haven't tested it though, just know it exists.
bind x select FromMouse_380+_Not_Aircraft_Not_WeaponRange_470_Weapons_Not_ManualFireUnit+_ClearSelection_SelectAll+
clear hawk
Sounds similar to how you can use tab to cycle through the unit types you have selected in starcraft which sounds really helpful. Not sure if I would want it to be the same key as selecting the control group though. Sounds like something widgetable for sure though.