The problem of differentiating between Inbox and Focus-Area can be solved by below Simple solution -
  1. Give option to make a space 'Default'
  2. Give the option to make a Folder and a List 'Default' under EACH space.
  3. While adding a Task,
3.1. When User leaves both space and List - empty -
Then task will go to the Default Space's -> Default Folder's ->Default List
3.2. When user selects space but leaves the list name empty -
Then Task will go to the Selected Space's -> Default Folder's -> Default List
Advantage -
  1. Inbox's current implementation can be left as it.
  2. Instead of having Single Inbox to gather the tasks - user will have so many options to choose where his tasks should go