Very sorry for the delay. With the rush to Imagine I am getting a bit behind on this group.
Magento is a full stack (frontend through to backend) and will stay so. However we are also opening up our APIs to make external integration easier. The thrust is around modularity and flexibility.
Magento will never be "we are APIs only, no UI". But if someone decides they want to use only our APIs for a production store, fine - go for it. We want to make our APIs available so you can do this. (You probably would keep our Admin UI in such cases still.)
So we are shipping more out of the box APIs, but we are also making it easier to glue your own APIs on top. REST, SOAP, AMQP (such as RabbitMQ) - we are making it easier to glue such APIs onto the code base. You might use this for integrations. You might use this with AngularJS single page apps if you want to. You might use this for mobile apps. We want to open the platform up to whatever the community can imagine.
It is similar in the M2 direction on HTML, CSS, etc. We provide HTML templates for all pages, but make them easy to replace. Business logic no longer lives in our HTML template files. We pulled out all inlined CSS as well. You can use our UI, or you can replace completely.
So it would be wrong to say "we are moving away from our UI strategy to an API based approach". But it definitely is "we are making M2 more flexible and more modular, to make it easier to use the parts of Magento you want". This is going to be an ongoing effort to improve upon iterativley.
