I'm definitely in favor of this idea, especially because of hiding items from "All Notes." I managed a family member's terminal illness, using Evernote to keep track of conversations with medical staff, etc. I do not want to lose this information, but I really don't want Evernote rubbing my nose in it every time I open "All Notes."
I suppose I can just export the contents of the notebook in question, and then remove it, but it would be a lot more convenient not to have to do this.