I think the current design does metaboxes a real disservice. The current layout and the section heading, "Extended Settings", makes it look and feel like a bit of an afterthought . Undoubtable many metaboxes uses will be able to be moved to their own block, but their will still be situations where whats contained under Extended Settings is essential to putting together a page but isn't appropriate as a block. In that case, Extended Settings, Just doesn't feel right and seems easily forgettable. That could create an awkward publishing experance, especially when those fields are required to publish.

Same goes with requiring the settings sidebar to be active for the metaboxes to be accessibly. Why? It seems that most of the extended settings wont interact with the sidebar, so why tie them together rather then allowing Extended Settings to remain sticky to the bottom of the screen.

I would also add that the minimalist white section headings for each metabox makes each section really hard to distinguish when editing. I understand this is early stages, but if it's not being considered I would say the design of this section needs a lot more work. Metaboxes now feel overwhelming and indistinct.