We spent a lot of time talking with the VCARDDAV working group while they
were working on vCard 4, and while several useful improvements to vCard 4
were made that brought it in closer alignment with PoCo, they ultimately
decided not to take a JSON version of vCard on as part of their charter.
Nevertheless, the specs are very similar, and there's good/easy 1:1
conversion code in both directions (see e.g.
http://www.plaxo.com/pdata/vcardTest), so there's not much difficulty in
currently using PoCo like "the un-official JSON format for vCard". Note BTW
that PoCo's JSON is intentionally much simpler and cleaner than the direct
JSON translation of vCard's XML format would be, since they opted for more
expressivity more mechanical 1:1 translation to their legacy serialization
format, whereas PoCo was more concerned with "looking good/simple on the
wire". Again, this is more a difference of style, since translating between
the two formats is easy in practice.