I must apologise for what may be random, incoherent mumblings, but here are a few thoughts that popped into my head ... and as such are influenced by our local circumstances and may not therefore apply universally.
A badge conveys a message about the holder, intended for an audience or audiences. If Moodle acts as "displayer" and a "issuer" of badges, there at least two sets of audience: internal to the organisation and external. Assuming for a moment that a Badge recipient will wish to display to both sets, then we in our school need to ensure that the badge can 'get out.' Not being familiar with the mechanics(electronics?!) of how that might occur, I'm more than aware that data pathways in and out of our organisation aren't always ... free-flowing ... for valid reasons! Ports, proxies, protocols and IP addresses are just a few of the terms with which I have just sufficient knowledge to know they might be significant. If Moodle is to 'push' Badges to an external backpack, can anyone tell me whether whatever is implemented is likely to be able negotiate a communication pathway between a typical(?) school internal Moodle implementation, to an external backpack provider? Or is the 3rd option suggested ("Don't implement the external backpack...") likely to be more effective, whilst clearly not providing the same degree of seamless experience for the Badge recipient as we might like? Thinking also about the 'Assertions' and specifically "...hosting a public key at a well known, public URL." In the case of a local Moodle behind a an educational Gateway, is this possible? Or will the 'key' be held externally from the school Moodle? Will it be taken care of during the Module design process? Or (as is likely!), is my understanding currently too limited?
On a separate, but related theme, if Badges are to carry 'weight' or have some degree of credence in more formal settings, it is likely that the 'audience' in those circumstances might want to inspect evidence of achievement - one of the 'optional' badge fields. Would I be right in thinking that this is where Mahara naturally sits? And if we don't have Mahara, we need to find an alternative way of surfacing the evidence produced en route to satisying the Badge criteria?
OK, brain starting to hurt.