Allow tasks to have no focus
A project consists of many steps and often the one "next action" must take place before any of the others can proceed. Those "blocked" actions don't really fit in "next", "inbox", or "someday". It would be useful not to have to give them any focus until they can actually proceed, or to give them their own focus called "held" or "blocked" or something like that. This makes review of the other focus areas simpler, quicker, and requires less remembering "oh wait I can't do anything with that task because it belongs to project Z and requires completion of another step before I can proceed on it".