In reply to wpezdeveloper.

If plugin dependency handling becomes a reality, and included in core, this could move WordPress in the direction where modules are slowly removed from core.

Should WordPress evolve against being a web or website(s) "operating system", taking the role as a "kernel" with a lot of APIs and a minimal "shell" (admin), then it's logical to include the REST API.

On the other hand, if WordPress is to evolve further as primarily a CMS, and basically having an mature, excellent and maximum flexible admin shell and internal theme API, then external facing APIs should become plugins. And plugins depending on it and so forth.

Currently both directions are open, and WordPress is moving at full speed in both directions. This may not be wise on a long term perspective. Some day a decision on the main direction has to be made.

As long as plugin dependency handling is not in core, then I think, for the best of encouraging it's use, is to get WP API into core as soon as possible. It may not only gain the development of new kinds of themes, but also "plugin apps" that live outside of WordPress itself (not loading WP), and even tailored administrative and content managing external applications. Plugin dependency handling may take a year or two. Then we can talk again.