echo this
"The biggest issue right now is that the REST API isn’t included in core,”

The WP REST API has been in development now for over 2 years now https://github.com/WP-API/WP-API/commits/develop?page=70

Over that time there has been 56 developers have made 2,244 commits.

@rmccue has done an enormous amount of work as the lead dev.

There was talk at one stage that it would be merged to core in wp v3.9 and hopes for every version since including v4.3 ... but still not.

WooCommerce got tired of waiting and released their own in feb 2014 - despite requests from wp to not release theirs until after the WP REST API was released in the core. The WC guys must have known that it was at that stage a long way off happening and went ahead anyway.

Last year we have built a number of WooCommerce child plugins with utilizing jQuery/Underscore/Backbone stack. couple of them
http://a3rev.com/shop/woocommerce-predictive-search/
http://a3rev.com/shop/woocommerce-carousel-slider/

But have not proceeded with any WordPress integrations because as David Wells wrote

"Telling users to install another plugin to run your plugin creates a real bad UX."

Re what Trevor Nelmes wrote:

"The BIG issue is security."

Whilst it is a top priority as it is with all software - The WordPress https://wordpress.org/plugins/json-rest-api/ has 10,000+ active users, which is a wonderful Beta - stable and seemingly secure

The WC JSON REST API which had a much shorter development cycle than the WP API is having has been in the wild for 18 months and is active on over 1 million sites without incident (sure their have been a couple of patches for disclosed vulnerabilities but nothing major)

My wish is that Matt and the Automattic team would make the WP REST API a much higher priority than what I think are peripheral features like the Customizer / shortstack / which seems to be the number 1 priorities.