In reply to wpezdeveloper.

Well, doesn’t that kinda make an argument for the REST API *not* being in jammed into core? That is, if it’s going to be an esoteric / fringe tool then isn’t that the classic use case for “make it a plugin”?

As far as I'm concerned, I'm not arguing for inclusion or non-inclusion in any way. I'm simply talking in terms of what the Theme Review Team will most likely see. One of our fellow teams needs some help, and we're happy to oblige, even if I don't think it'll do much to help.

To answer the question though, no, that doesn't make it a case of being plugin territory. It's a huge ROI risk for theme authors to spend the time on something that's not baked into core. It'll always be a fringe tool for theme authors as a plugin because WP has no dependency system.

Now, we can talk about WP's lack of a dependency system, but the reality is that the REST API has been built. It could be years, if ever, before we see any sort of dependency system. Without either that or core inclusion, the REST API simply isn't going to be utilized by many theme authors.

If it's in core, you'll see a lot more themes using it in some fashion.