Proposed resolution:

This wording is relative to N4750.

1. Change [span.overview], class template span synopsis, as indicated:

   namespace std {
     template<class ElementType, ptrdiff_t Extent = dynamic_extent>
     class span {
     public:
       // constants and types
       using element_type = ElementType;
       using value_type = remove_cv_t<ElementType>;
       using index_type = ptrdiff_t;
       using difference_type = ptrdiff_t;
       using pointer = element_type*;
       using const_pointer = const element_type*;
       using reference = element_type&;
       using const_reference = const element_type&;
       using iterator = implementation-defined;
       using const_iterator = implementation-defined;
       using reverse_iterator = reverse_iterator<iterator>;
       using const_reverse_iterator = reverse_iterator<const_iterator>;
       static constexpr index_type extent = Extent;
     
       […]
     };
     […]
   }
   

[ 2019-01-20 Reflector prioritization ]

Set Priority to 0 and status to Tentatively Ready

std::span does not have a typedef for const_pointer and const_reference. According to Marshall Clow, this is merely an oversight.