Proposed resolution (July, 2009):

Change 13.9.4 [temp.expl.spec] paragraphs 15-16 as follows:

An explicit specialization of a static data member of a template is a definition if the declaration includes an initializer; otherwise, it is a declaration. [Note: there is no syntax for the The definition of a static data member of a template that requires default initialization. must use a braced-init-list:

  template<> X Q<int>::x;      // declaration
  template<> X Q<int>::x ();   // error: declares a function
  template<> X Q<int>::x {};   // definition

This is a declaration regardless of whether X can be default initialized (9.5 [dcl.init]). —end note]