When both learners and organizations come to badges, one of the first questions they ask is how badges differ from credentials, diplomas, certificates, or the other tools currently used to mark when learning has occurred. This is the primary question that people new to badges need addressed. Currently, addressing that question requires a technical vocabulary lesson before the actual utility of badges can be addressed.
Eliminating the backpack (as both a technical requirement and a metaphor) would simplify things. Without the backpack, we have a system where badges are earned and badges are displayed. The logic of how badges are earned, stored, and displayed could be left where they belong: to the sites where badges are both earned and displayed.