In reply to Matt B.

I wouldn't doubt that most theme and plugin makers waited until the 5.0 beta to start working on Gutenberg compatibility (which in my opinion is reasonable). We didn't wait, so we've had a significant head-start, but I'm still not sure we'd be able to make things what they ought to be by the 19th. Fortunately I don't see the 19th happening as there are only five or six work days left and there's no RC yet.