WordPress.org themes and premium WordPress themes differ in scope. The former is narrow and only handles styling and layout, the latter is supposed to be a one-stop-shop for a website. Good premium themes:
- Solve a specific problem. They don’t try to do everything and instead, decide their limitations based on the use-case they’re solving for
- Are integrated with plugins that help solve the said problem
- Keep the users safe from themselves — by helping them take good design and plugin decisions, and itself — by not locking the users in.
By adding extensive customizability Gutenberg seems to be shifting these responsibilities from the theme to the user. Premium themes have long been responsible for moving the WordPress platform forward, the changes brought by Gutenberg might negatively affect this landscape.