I've operated on the assumption that the Nov 19 deadline is like many Gutenberg projected release dates in the past: a target, and something that adds urgency for both the Gutenberg team and third party theme/plugin developers. But ultimately not realistic and bound to be deferred.

To the powers that be: if you're seriously considering a Nov 19, please, please do not.

Gutenberg is no where near ready. There are bugs, even for obvious, vanilla use cases, not to mention edge cases. Theme and plugin developers are not caught up or ready. Even for plugin developers who are working hard to be ready, the api still changes and breaks things frequently in recent releases.

Gutenberg is not a normal release - it profoundly alters the core UI on 30% of the internet, often in ways that are not backwards compatible. For a release of this magnitude, the product itself should be fully 100% ready, first (which it is not), and then it should site out there for 3-6 months while the ecosystem prepares for it.

And the idea that it's been widely tested is such a strange thing to say - because it's the testing itself that still shows it's not ready. Just being tested a long time is not the goal - the goal of testing to ensure it's 100% stable, well-liked, and won't break third party integrations. Testing to date still shows the opposite.

I'm fond of Gutenberg. But a premature release would be a disaster of epic proportions for the entire WordPress ecosystem. And Nov 19 is clearly, definitely premature.