Block based Themes are coming to WordPress sooner or later and we just published the first “beta” release of our Full Site Editing Starter Theme.
If you see yourself as an early adopter who likes to get his/her hands dirty feel free to generate a copy via the Theme Generator: https://them.es/starter-fse
The source code is licensed under GPLv2 and has been published on GitHub.
Full Site Editing is a collection of features that allow to fully customize a WordPress site via a new site editor. Overall the Full Site Editing experience using block based Themes looks promising and already works pretty well but you need to be aware that not all features are final and that bugs will appear during development.
Now a 100% (!) PageSpeed score is achievable with WordPress. Even on Mobile: https://developers.google.com/speed/pagespeed/insights/?url=https%3A%2F%2Fthem.es%2Fstarter-fse%2F
At the current state this Starter Theme is not recommended for production sites. Please use it at your own risk and provide technical feedback to the Gutenberg team if possible!
One more thing: Block based features are still in development and have not yet been fully integrated in WordPress core. In order to enable the Site editor you need to install the Gutenberg Plugin on your site.