In reply to Nick.

Right now, Gutenberg is not ready mostly due to the performance issues no one working on it has bothered to test in the past year. Adding custom blocks into the mix will make things only worse.

The only way for Gutenberg to be ready in the next 2 months (January fallback date), is for the development on Gutenberg finally gets frozen. Since the merge into the core started, we got at least 3 new Gutenberg versions, each one adding new features, and all that was fast-tracked into the core, with very little testing. Gutenberg has to be frozen as is, and only bug fixes and performance improvements can be added to it - no enhancements to the UI, new blocks or changes to menus.

For as long as Gutenberg is continuing with normal development, and every change gets to go to the WP core, it will never get ready, and if WP is shipped like that in January, it will be a very buggy product, untested with a large number of custom blocks, untested for long and complex content.

But, that is one argument no one working on Gutenberg seems to grasp, and they are continuing to add features, instead of focusing only on fixes.