If the Shib SP were to go support https://issues.shibboleth.net/jira/browse/SSPCPP-717 then the MDA should generate a JSON encoded /DiscoFeed equivalent of all IdPs that the MDA knows about, ready to be published. The JSON would have to be signed, of course, so maybe something JWS-ish?
FWIW, the actual code for the JSON generation is brute force code inside the DiscoverableMetadataProvider class in OpenSAML. The handler in the SP really just aggregates all those and handles the caching.
If the Shib SP were to go support https://issues.shibboleth.net/jira/browse/SSPCPP-717 then the MDA should generate a JSON encoded /DiscoFeed equivalent of all IdPs that the MDA knows about, ready to be published. The JSON would have to be signed, of course, so maybe something JWS-ish?
Worth considering, or not?