Hi,
Gutenberg removed the hook for meta boxes after title, and there's no way to do that. The WP team said that they will turn the post title into a block itself, so there's no fixed position.
It would be nice to have a MB Block (reusable?) selectable or a separate one for each MB Group/Field one could place in the Block column so you could edit in full width.
Can you explain this? I'm not sure I got it.