In issue 15316 (msg168896, Brett Cannon):

  Create a ModuleNotFoundError exception that subclasses ImportError
  and catch that (breaks doctests and introduces a new exception that
  people will need to be aware of, plus the question of whether it
  should just exist in importlib or be a builtin)

While it's too late to go into 3.3, this is a reasonable addition for 3.4.  Perhaps other ImportError subclasses are warranted, but they can be addressed separately.