an easy but a bit ugly solution is creating a mod that changes the leg(-colour) while kneeling
so if a soldier kneels his/her legs look slightly-noticable different
that would help me with getting an easy overview who of (all) my soldiers is kneeling
+ only need a mod - no code change required
+ you can see the kneeling state for all soldiers
- its not the best solution from a UI perspective
- it also needs work for all armours that are added via mod