JSON serialization of SD-JWT VC isn't actually usable in practice

When defining the SD-JWT VC profile, https://openid.net/specs/openid4vc-high-assurance-interoperability-profile-1_0.html#section-6.1-2.1 says:

Compact serialization MUST be supported as defined in [RFC9901]. JSON serialization MAY be supported.

I think 'JSON serialization MAY be supported.' isn't a useful statement. It doesn't say who may support it. There is no defined way for verifiers to say they support it, so I think the wallet can't ever sensibly returned the JSON serialisation.

There were various discussions about this ( https://github.com/openid/OpenID4VC-HAIP/issues/31 / https://github.com/openid/OpenID4VC-HAIP/pull/46 ) - in the PR it was originally:

JSON serialization MAY be supported if required by the jurisdiction

but then got changed to drop that jurisdiction clause. JAdES-style long-term validation and issuer multisig were cited as reasons to support JSON serialization. But I can't see an interoperable way to actually do it, so deleting the 'JSON serialization MAY be supported.' might be the best outcome.

Read section 6.1-2.1 of the HAIP specification and RFC9901, then review the related discussion in issue 31 and pull request 46. Determine whether JSON serialization can be advertised interoperably, and update the profile wording and related references to reflect the agreed rule.