I dont think is bug just war crime

Can you explain what's the issue with this?

Target identification is a nightmare in MP with both friend and enemy able to wear either uniform, carry any weapon and drive any vehicle. It's hard enough to tell friend from foe when half the players are running around in their underwear, let alone wearing each other's uniforms.

Bohemia deliberately removed the feature from Arma 3:
Dan [Musil, Project Lead]: We decided to limit this only to uniforms affiliated with a player's side. Although we were considering allowing the player to don any uniform at the start of development, it appeared that such generality would bring some very complex issues with AI and multiplayer rules. Also, it is against the Geneva Convention.

Wich means there is big chance they will remove it again in next patches..ehm early acces ?

It would be good to have armbands.

I would suggest this function to be make optional and on per default for "normal" armies vs armies. But there are also other gamemodes and mods (hopefully), e.g. Lootshooter, Survival, etc.