Feel free to add to the todo lists
- Caps - allow users with post edit capabilities to build templates
- authors should only able to edit own template
- AJAX-saving blocks
- Enable builder to operate inside post editor
- SEO plugins like Yoast can't read inside shortcode, add support to that
- Bulk actions
- Localize all missing translatable texts (in blocks, etc)
- Move template manager on a separate section, preferably similar to how it's done on Menus
- UI minor revamps to follow current WP UI
- Visual Editor
- Template duplications
- Localization