The site editor currently has the ability to export the user's templates and template parts. The implementation, however, was put together just to allow easier flows during development and the initial days of sharing block themes. As things mature, we need to revise all the implications of exporting properly.

• Capabilities should be matched with the expectations of core WP. Currently the endpoint is locked behind edit_theme_options but it should be switched to export at the very least. We might want to consider a new capability download_theme (to complement upload_themes) or export_design, particularly with the next point...
• Include user modifications to theme.json configuration. We have the opportunity to make the customizations applied to global styles also part of the export flow so that it can easily be migrated to another site, let's make sure to include this in the consideration.
• In terms of interface, we should probably relocate all of this into the main Tools > Export section of the admin instead of a custom flow in the editor and ensure it's extensible like other export tools.