Your comments

Yeah, that would be a sane assumption and would work without much trouble. It would also help deal with spam, since github has mechanisms to disable spam repositories etc.
Well true, but anyone could forge an url with .json at the end and it would be quite dangerous to have N instances of XDM polling random addresses for json. This could easily be used as an attack against servers, the ultimate DDOS :)

Not to mention that you can quite easily forge an url that is valid but has nothing to do with json, but still looks like json: or

The way that PHP works, that should be valid with pretty much all php files with the same logic.

Don't get me wrong, I like the idea of decentralized repository management, but I'm seeing a lot of potential for malicious behavior with the proposed solution.
Let me object to this in the form of a tweet:

@XDM_APP Buy my fancy viagra now

Sure, it might be a nice and dynamic solution, but we need some kind of a way to control and remove harmful entries as well.