Proposed resolution:

This wording is relative to N5008.

1. Modify [format.range.formatter] as indicated:

   namespace std {
     template<class T, class charT = char>
       requires same_as<remove_cvref_t<T>, T> && formattable<T, charT>
     class range_formatter {
       […]
       template<ranges::input_range R, class FormatContext>
           requires formattable<ranges::range_reference_t<R>, charT> &&
                    same_as<remove_cvref_t<ranges::range_reference_t<R>>, T>
         typename FormatContext::iterator
           format(R&& r, FormatContext& ctx) const;
     };
   }
   

   […]

   template<ranges::input_range R, class FormatContext>
     requires formattable<ranges::range_reference_t<R>, charT> &&
              same_as<remove_cvref_t<ranges::range_reference_t<R>>, T>
   typename FormatContext::iterator
     format(R&& r, FormatContext& ctx) const;
   

   -11- Effects: Writes the following into ctx.out(), adjusted according to the range-format-spec:

Currently, the signature of `range_formatter::format` is as follows:

template<ranges::input_range R, class FormatContext>
  requires formattable<ranges::range_reference_t<R>, charT> &&
           same_as<remove_cvref_t<ranges::range_reference_t<R>>, T>
typename FormatContext::iterator
  format(R&& r, FormatContext& ctx) const;

which requires that the reference type of the range parameter must be `formattable`, and such type must be exactly `T` after removing the cvref-qualifiers.

However, satisfying the latter always implies satisfying the former, as the `range_formatter` class already requires that `T` must be `formattable`.

There is no need to perform a redundant check here.