I'm currently rebuilding a very complex designer-built site using gutenberg that is a horrible mix of x-theme, visual composer plus other third party layout / editor tools. Gutenberg should resolve a lot of issues and make updates less problematic. But my biggest concern is the release date. End of year is always frantic with high workloads. The thought of receiving hundreds of unexpected support calls from clients in November is very scary. Mid January or early February much better.