It would be nice to be able to create/add a new notebook in a stack right from the sidebar context menu, rather than having to navigate to the Notebooks screen. Switching contexts is painful.
See the screenshot...along with "Expand Stack", why not have "Create Notebook"?
Also, it would be nice to be able to drag around notebooks between stacks right from the sidebar. Why do we need to go to the Notebooks screen each time to do this? I think it's way more natural to be able to manage notebooks right from the sidebar where you can see the structure clearly.