In reply to Jonathan.

A meta box at its core, is just a visual piece of UI for interacting with something in WordPress. It may seem crazy, but the reality is that most likely all meta boxes will be replaceable with blocks, and with the client rich experience being provided by blocks, most meta boxes, if not converted, will probably eventually be made irrelevant by a superior block implementation by another vendor.

It is definitely hard to see how that would work, but I will definitely be posting some examples on my blog before the end of the year to show how meta boxes can be re-envisioned as blocks, and why it would possibly be a better experience for everyone.