The latest development releases of Parse::CPAN::Meta now support both META.yml and META.json files. By default, it uses JSON::PP for the META.json files. Accordingly, JSON::PP has just been added to the Perl core. (Thank you to Makamaka for his work getting JSON::PP ready for bleadperl.)
There's more work on the horizon, but I expect to get full support for the version 2 CPAN::Meta::Spec into Perl 5.14 before I'm done.