How about dynamic player customization, similar to the music system? If your team is doing great, it will spawn in shiny clothes and gear, however if you take a lot of losses, your team starts to spawn with bandages.
The further a battle progresses, the more dirty the clothing becomes and the more common bandaging is on both sides, since it is an equal struggle of both sides. This would also have a tactical benefit of helping the loosing team a little, since dirty clothes mean harder recognition and clean shiny clothes mean easy spotting that glowing helmets.
I do not recommend facial customization, since people tend to do silly stuff with them, if they are possible. Something like ArmA, where you can choose your face would be enough, I think. Of course things like helmet customization for the sniper and assault classes or different camouflage on clothes for veterans might be desired and reasonable. What about something as "simple" as wearing medals into battle?