In reply to Rarst.

I think a lot of the uncertainties are coming from the fact meta-boxes represent different concepts:

* Things that might be transformed into blocks.
* Current meta-boxes reimplemented as JS modules to extend Gutenberg UI.
* Current meta-boxes working as they are.
* Custom fields applied through blocks.
* Custom fields applied through meta-boxes.

We are not purposely trying to break anything that works! Shortcodes, custom fields, etc, will continue working. I also hope we can improve on them, like the shortcode block that currently exists in the plugin. The UI to interact with them might change (unless you disable Gutenberg completely), and certain use cases for meta-boxes are going to be a better fit for blocks going forwards. With the technical changes we also need to see what is the most viable approach.