Proposed resolution:

Add the following to basic_iostream's class synopsis in [iostreamclass], immediately after public:

  // types:
  typedef charT                     char_type;
  typedef typename traits::int_type int_type;
  typedef typename traits::pos_type pos_type;
  typedef typename traits::off_type off_type;
  typedef traits                    traits_type;

Class template basic_iostream has no typedefs. The typedefs it inherits from its base classes can't be used, since (for example) basic_iostream<T>::traits_type is ambiguous.