In reply to Matt B.

.. that put off even getting started with Gutenberg until the 1st WP 5.x beta. That was a mistake IMO.
It simply was and is not possible to seriously develop for Gutenberg. Way too many bugs, heavily changing UX over last year, many very breaking changes, deprecated features every few weeks, new APIs added besides "feature freeze" e.g. "Annotation API" today, and whatnot.

All you can do today is testing a few small blocks, which is no serious development. Everything else is waste of time and sunk costs.

It is not possible to offer "Gutenberg ready" themes and plugins, as long as Gutenberg is not ready.