It would fuction as the current external files for NPC's: A "badges" file would determine just the name an the sprite to use ingame inside the textures folder of a resourcepack and put that item inside the badge tab inside creative. An aesthetic "useless" item should be reather simple to implement (I don't know programing so it's just my guess) and would make servers able to open player gyms with their very own designed badges by just asking the users to download a resourcepack addon.
Opinions?