Suggested resolution:

Change in 13.2 [temp.param] paragraph 14 as follows:

... If a A template-parameter pack of a function template declares a template parameter pack, it shall not be followed by another template-parameter P unless

• that template parameter P is deducible from the parameter-type-list (9.3.4.6 [dcl.fct]) of the function template or ,
• P has a default argument (13.10.3 [temp.deduct]), or
• that template parameter pack is also a pack expansion.

...

(From submission #666.)

Consider:

  template <class Head, class... Tail>
  struct test {
    template <Tail..., Head>
    static void make() {}       // clang accepts, MSVC rejects
  };

  int main() {
    test<char, int, float>::make<4, 6.f, 'a'>();
  }

There is implementation divergence for the treatment of this example. It ought to be allowed.