I want this too.Good description of your idea.

Mine and another similar post:
http://sublimetext.userecho.com/users/120696-michael-kaiser-cross/feedback/
http://sublimetext.userecho.com/topic/79741-it-should-be-possible-to-organize-sidebar-items-into-custom-categories/

ya i agree. folders within projects. basic but necessary

Actually no. With that option you can only add folders that exist on your computer. What I am talking about is being able to add text files from two different filesystem folders and add them to a "virtual folder" inside a project. Basically projects within projects or "project folders".