View All Things/Tasks & Who They're Assigned to.
Have a quickview tab of some sort that shows all the tasks, no matter who they're assigned to or what list they're under. Then have the ability to filter them according to who they're assigned to, etc.
You can do this already by creating a saved search list using the Advanced Search facility. Select all lists and it will give you one list with all tasks and you can then 'Stack By' or 'Group By' however you like e.g. Priority, Deadline, or Assigned to... Hope this helps!