We are working on making Drupal 8 truly API-first: API-first initative.

We are:

Improving Drupal 8's REST API, to become to become usable by 8.2.0 (done!) and then best-in-class by 8.3.0 + 8.4.0.
Bringing JSON API support to Drupal 8 core (experimental in 8.4.0).
… and there's so much more we'd like to see happen, such as: GraphQL, OAuth 2, UUID/revision support, CouchDB support. 
In doing so, we need:

frustrations! to hear where Drupal 8's REST support in core (and contrib) is currently failing, in terms of DX, capabilities, and so on.
roadmap feedback. (We need to hear what you think is important and why.)
help! We can provide mentoring: if you help out with patches, we'll provide reviews to help you land things in core!
This is an update of the session in Dublin. At this core conversation:

We'll start with a succinct overview of what's going on, what has happened so far, and our long-term ambitions. Then we'll open the floor for discussion! When necessary, we'll explain subjects in more detail.
You don't need to be an expert in anything, just rudimentary knowledge about web services is sufficient.
You'll walk away knowing what's happening in the API-first initiative, and will hear about other attendees' concerns/thoughts/requirements/….