I wonder if you are familiar with restconf, which is NETCONF over HTTP
with the YANG data in either XML (which is what NETCONF uses for its RPC
and data therein) or in JSON.
Certainly (RESTCONF is the basis of COMI in the CoRE WG).
The YANG-JSON mapping is solving a different problem than the one that
was discussed here: It is representing data that conforms to a YANG
Model in JSON (where that data previously has been represented in XML).
So it does not have to cope with all the strangeness of XML, but only
with those parts of XML used by YANG.
Some complexities in YANG-JSON come from the fact that YANG has been
designed in a way that is a bit too XML-friendly, and that YANG-JSON
tries to be I-JSON (RFC 7493), so it can only use a subset of JSON.
(The core of COMI is a YANG-CBOR mapping, which will inherit some of the
former, but we hope none of the latter class of problems.)
Grüße, Carsten