Many of Gutenberg's add_theme_support() options are already available to define in experimental-theme.json:

• disable-custom-font-sizes
• disable-custom-colors
• disable-custom-gradients
• editor-color-palette
• editor-gradient-presets
• editor-font-sizes
• custom-line-height
• custom-units
• custom-spacing
• experimental-link-color

The rest should be made available there as well:

• align-wide
• core-block-patterns (opt-out)
• editor-styles
• dark-editor-style
• post-thumbnails
• responsive-embeds
• wp-block-styles