@vfxdude this functionality won’t likely be replaced by Gutenberg so much as better integrating Gutenberg and Customizer functionality. You’ll start to see more and more of the functionality of the two merge together into an optimal end state of a seamless inline / front-end editing experience (that’s still awhile away, but a goal nonetheless).
As you find bugs in testing Customized Posts (while using Gutenberg or not), it would be great if you could add them as issues in the Customize Posts GitHub repository here: https://github.com/xwp/wp-customize-posts/issues.
Otherwise, if you have questions on Customize Posts functionality we can handle those here… thanks!
Gutenberg will open up a lot of opportunities for inline editing on the frontend (in the Customizer preview); styling is an open issue that still needs to be addressed.
I think that the UI aspects of Customize Posts will be eventually made obsolete with Gutenberg being merged into the Customizer, but that process could include aspects of Customize Posts as part of the core merge, such as the architecture for modeling posts and postmeta as Customizer settings.
So while integration happens between Gutenberg and the core Customizer, I do think that the Customize Posts plugin itself will increasingly be less relevant as the features are merged into core as part of the integration.
