I'm a premium member because I use Evernote as an individual. One of the great concepts that's featured on the business model, is the ability to separate "Business" Notebooks & "Personal" Notebooks. I think it would be very effective to provide a similar feature to the Premium model, where users can separate notebooks per two or three main categories or "filing cabinets". For example many of my notebooks and notebook stacks are created for various clients, per my sales job. On the other hand, various notebooks and stacks are created per my real estate investments. Lastly, I have a group of notebooks that a all geared toward my hobbies and personal development. All of my notebooks and stacks, whether they're a subject dealing with sales, investments, or personal hobbies, are all grouped in alphabetical order in the left window column under one heading "Notebooks."
It would be very effective to have an option to separate major categories of notebooks under separate headings or tabs; similar to what I would do if I were filing all of my notes in filing cabinets. I'd have one filing cabinet for my sales notebooks, another for my investment notebooks, and a third for my miscellaneous notebooks. I'm hoping this is possible to develop as I think it would help add another layer to my organization and also a feature to the premium model service.