In reply to T Piwowar.

The number of developers contributing to the WordPress project has increased since the integration of Gutenberg. Major plugin developers have adopted the block editor and are building interesting things with it. Right now, the signs point to Gutenberg being a boon to development. Maybe I'm a bit of an optimist, but I don't see the project being detrimental to future growth.

As the project continues, it has the potential for massive growth in development activity if core can finally solve the Fields API question. What I mean by this is Gutenberg could standardize how developers build anything within WordPress. Competing APIs have been a large hurdle for developers over the years. And, Gutenberg added another. The question is whether everything will eventually coalesce into a standardized API for any admin screen.

Personally, I would have rather seen this happen before Gutenberg, but the idea never gained enough traction on its own.

As for the customizer, I'm not sure what major features it is missing. However, I could see it falling to the wayside as we move into full-site editing via the Gutenberg project. Or, the two APIs melding in some way. It's hard to say at this point.