Proposed resolution:

This wording is relative to N5014.

1. Modify [simd.ctor] as indicated:

   template<class U> constexpr explicit(see below) basic_vec(U&& value) noexcept;
   

   -1- Let `From` denote the type remove_cvref_t<U>.

   […]

   -4- Remarks: The expression inside `explicit` evaluates to `false` if and only if `U` satisfies convertible_to<value_type>, and either

   1. (4.1) — `From` is not an arithmetic type and does not satisfy constexpr-wrapper-like,

   2. (4.2) — `From` is an arithmetic type and the conversion from `From` to `value_type` is value-preserving ([simd.general]), or

   3. (4.3) — `From` satisfies constexpr-wrapper-like, remove_cvref_tremove_const_t<decltype(From::value)> is an arithmetic type, and `From::value` is representable by `value_type`.

`decltype(From::value)` would be const int& if `From` is a type of std::cw<42>, so the reference also needs to be removed for checking the arithmetic type.