Hi,
I got an idea about backpack textures, function to add different Headtexture for each player or GUI menu with choosing those skins for backpacks. So players may have different textures.
It's simple, it should be (for example) like that:

#(default) 
HeadTextureValue: "eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvOGRjYzZlYjQwZjNiYWRhNDFlNDMzOTg4OGQ2ZDIwNzQzNzU5OGJkYmQxNzVjMmU3MzExOTFkNWE5YTQyZDNjOCJ9fX0=
default: true"

#custom 
BackPack2:
permission_needed: minepacks.skin.backpack2 
default:false

#custom 
BackPack3:
permission_needed: minepacks.skin.backpack3 
default:false

There can be also priority system, so if you have permission for the second one backpack skin, it will always rewrite player's texture by that one with highest priority. Or just player can choose from (again example) /backpack skins gui menu. In this menu would be select skin method.
It is more advanced, better and interesting, cuz people love skins hah..and it cab bring really a lot of fun.

Minepacks v3.0 will have the option to change the backpack skin and even allow custom models.