Taken literally, Clause 13 [temp] paragraph 2 does not permit operator functions to be templates:

In a function template declaration, the declarator-id shall be a template-name (i.e., not a template-id).

and, in 13.3 [temp.names] paragraph 1, a template-name is defined to be simply an identifier.

Issue 301 considered and rejected the idea of changing the definition of template-name to include operator-function-ids and conversion-function-ids. Either that decision should be reconsidered or the various references in the text to template-name should be examined to determine if they should also mention the non-identifier possibilities for function template names.