i would personally like something that is being asked here. problem is, consistencies. or rather, inconsistencies. and the huge work that it requires.
devs partially tried to address this, or open the possibilities for the future.
for example, on the soviets models, the rank over the shoulder have different textures. meaning that you can add new ranks as textures for those pieces:

both for the GE & US patches system were created.
allowing squad insignias and ranks appear on their tunics:

but, they discontinued such system for unknown reasons.
the problem however, comes with japan and italy. or technically, also UK.
their tunics / torso do not have separated ranks or patches system.
meaning that, you’d actually have to edit the textures of the whole outfit.
which means, having to create 4 textures for each rank.
aka change the texture _N*, texture _D*, Cmask* and _ao*
just for one rank.
it can be sort of time consuming for something that they haven’t really considered.
next problem is, you’d have to make the cosmetic system even more complex.
because you’d have to keep in mind the soldier rank across 200+ squads.
so that they can wear specific items
which, they didn’t do for medical equipment.
no medics can wear medic helmet or tunic outside the base squads. because cosmetics are squad based.
so, if anything, and if we’re lucky, we’ll be the ones deciding who wears what.
and it will results in players running with all staff sargs on a squads.
just like the volkssturm outfit.
where everyone is a squad leader ( lol )