Proposed resolution:

This wording is relative to N4861.

1. Modify [range.refinements] as indicated:

   -5- The viewable_range concept specifies the requirements of a range type that can be converted to a view safely.

   template<class T>
     concept viewable_range =
       range<T> && (borrowed_range<T> || view<remove_cvref_t<T>>);
       ((view<remove_cvref_t<T>> && constructible_from<remove_cvref_t<T>, T>) ||
       (!view<remove_cvref_t<T>> && borrowed_range<T>));