I believe Clang is correct to produce this error:
The [temp.inst] section of the C++ standard in paragraph 10 says:
If a function template or a member function template specialization is
used in a way that involves overload resolution, a declaration of the
specialization is implicitly instantiated (14.8.3).
Forming the implicit conversion sequence necessary to rank the overload candidates for the call to TYPE_VALUE’s constructor requires the instantiation of the conversion operator. And the use of an incomplete type parameter to the trait doesn’t form an invalid type, so this isn’t a substitution failure, it is a hard error.