Proposed resolution:

Wording relative to the post-202106 working draft (as near as possible). This PR is currently being implemented in MSVC.

1. Modify [range.istream.view] as indicated:

   namespace std::ranges {
     […]
     template<movable Val, class CharT, class Traits>
       requires default_initializable<Val> &&
                stream-extractable<Val, CharT, Traits>
     class basic_istream_view : public view_interface<basic_istream_view<Val, CharT, Traits>> {
       […]
       Val value_ = Val(); // exposition only
     };
   }
   

[ 2021-10-14 Approved at October 2021 virtual plenary. Status changed: Voting → WP. ]

[ 2021-06-23; Reflector poll ]

Set status to Tentatively Ready after seven votes in favour during reflector poll.

P2325R3 removes the default member initializers for basic_istream_view's exposition-only stream_ and value_ members. Consequently, copying a basic_istream_view before the first call to begin may produce undefined behavior since doing so necessarily copies the uninitialized value_. We should restore value_'s default member initializer and remove this particular footgun.