when will "scoped template specalization" be available? gcc trunk seems not support it

[Dennis Luehring]

i've read that scoped template specalization is allowed in C++17 - is it
planned for the next gcc release?

otherwise i will switch to an if constexpr solution - but would be still
to have this feature

checked compiler:

gcc trunk (and latest intel) do not support it
clang (starting with release 7) and MSVC (starting with VS2017(i don't
know the exact revision)) supports it

------
enum class E{ A };

struct Ta{ int x; };

struct Mapper
{
     template<typename Type>  struct type_to_enum{};

     template<> // <-- FAILS
     struct type_to_enum<Ta>
     {
         static constexpr auto value = E::A;
     };
};