Stack Exchange badges are limited in the sense that they are only easy to view and display on the associated Stack Exchange sites. A user wishing to display their badges to the world generally must do so by linking to the associated Stack Exchange profile(s).
There is an open-source framework for issuing digital badges that can be displayed in a wide variety of venues, either on their own or aggregated with badges from other sources in an integrated format such as an online resume.
Stack Exchange sites should provide an option for users to receive their badges as Open Digital Badges. These are highly extensible and can be grouped according to the wishes of the issuer. Most likely, the badge class would be indicated in the badge metadata as well as shown in the badge image (for example, a gold badge would, well, be gold or at least have gold coloration in it).
One concern I have is that tag badges might not fit well as Open Badges because tag badges, unlike regular SE badges, are revocable under non-extraordinary circumstances, and Open Badges are designed to be issued once for all time. Perhaps tag badges could be excluded, or special qualified Open Badges could be issued indicating (for example) that such-and-such a tag badge was achieved on a certain date.
