Do you think you (as GP) would build your own Page Builder (like Site Origin or Elementor) to sit within WordPress 5 Block Editor? Or is a later version of the Block Editor going to support more custom WYSIWYG page building? (Like blocks aligned in columns)
Aside of the simple Sections builder we won’t be developing any ‘pagebuilder’. Instead we are focusing on developing features and Blocks for the new editor. You will see that the GP Theme has already been integrated with Gutenberg providing editor styles to match your front end styles.