http://json-ld.org claims to be a format of JSON to organize and link data on the web. HTML already provides a way to link data with the <a href> tag and microformats (in this case h-card and xfn) already provide a way to add additional machine readable semantics.

_simple-example.json

{
  "@context": "http://json-ld.org/contexts/person.jsonld",
  "@id":      "http://dbpedia.org/resource/John_Lennon",
  "name":     "John Lennon",
  "born":     "1940-10-09",
  "spouse":   "http://dbpedia.org/resource/Cynthia_Lennon"
}

simple-example-with-decoration.html

<div class="h-card">
  <a href="http://dbpedia.org/resource/John_Lennon" class="u-url u-uid p-name">John Lennon</a>
  was born on
  <time class="dt-bday" datetime="1940-10-09">October 9<sup>th</sup>, 1940</time>
  and was married to
  <a rel="spouse" href="http://dbpedia.org/resource/Cynthia_Lennon">Cynthia Lennon</a>.
</div>

simple-example-without-decoration.html

<div class="h-card">
  <a href="http://dbpedia.org/resource/John_Lennon" class="u-url u-uid p-name">John Lennon</a>
  <time class="dt-bday">1940-10-09</time>
  <a rel="spouse" href="http://dbpedia.org/resource/Cynthia_Lennon">Cynthia Lennon</a>
</div>

Very nice, but you should probably add

Yoko Ono

:)

Comparing against RDFa is also helpful:

<div vocab="http://schema.org/" 
  about="http://dbpedia.org/resource/John_Lennon" typeof="Person">
  <span property="name">John Lennon</span>  was born on
  <time property="born" datetime="1940-10-09">October 9<sup>th</sup>, 1940</time>
  and was married to
  <a rel="spouse" href="http://dbpedia.org/resource/Cynthia_Lennon">Cynthia Lennon</a>.
</div>

For fun, take the HTML markup above and dump it into http://rdfa.info/play/ to visualize the data.

HTML already provides a way to link data with the A-HREF tag and microformats (in this case h-card and xfn) already provide a way to add additional machine readable semantics.

I think you might be missing the point of JSON-LD... it's meant to be used primarily for REST Web APIs and storing Linked Data in document-based storage engines. Sending HTML back and forth to do your REST Web API calls or storing HTML in a database as your primary data format isn't the best way to go about exchanging Linked Data. :)

@msporny "isn't the best way" doesn't count as a good argument. Try again. ;)

JSON is a common data format. The data parsed from Microformats 2 is described in terms of its JSON representation: http://microformats.org/wiki/microformats-2-parsing. Data is transformed between a variety of representations all the time - such as for this web page you're now reading, which is generated by interpolating the appropriate data from a database into the HTML. If people want a JSON view of my data without the HTML that they can use their JSON parsers / databases on, I don't see the harm in accommodating them.

You can see an example of this in action on e.g. http://calagator.org/events/1250464699, where the same data is available in microformats, microdata, JSON, and XML formats, or on my home page.