Proposed resolution, March, 2018:

Change 9.6 [dcl.struct.bind] paragraph 3 as follows:

Otherwise, if the qualified-id std::tuple_size<E> names a complete type, the expression std::tuple_size<E>::value shall be a well-formed integral constant expression and the number of elements in the identifier-list shall be equal to the value of that expression. Let i be an index prvalue of type std::size_t corresponding to v_i. The unqualified-id get is looked up in the scope of E by class member access lookup (_N4868_.6.5.6 [basic.lookup.classref]), and if that finds at least one declaration, the initializer is e.get<i>(). Otherwise, the initializer is get<i>(e), where get is looked up in the associated namespaces (6.5.4 [basic.lookup.argdep]). In either case, get<i> is interpreted as a template-id. [Note: Ordinary unqualified lookup...

[Accepted as a DR at the June, 2018 (Rapperswil) meeting.]

According to 9.6 [dcl.struct.bind] paragraph 3,

Otherwise, if the qualified-id std::tuple_size<E> names a complete type, the expression std::tuple_size<E>::value shall be a well-formed integral constant expression and the number of elements in the identifier-list shall be equal to the value of that expression. The unqualified-id get is looked up in the scope of E by class member access lookup (_N4868_.6.5.6 [basic.lookup.classref]), and if that finds at least one declaration, the initializer is e.get<i>(). Otherwise, the initializer is get<i>(e), where get is looked up in the associated namespaces (6.5.4 [basic.lookup.argdep]). In either case, get<i> is interpreted as a template-id.

It is not clear what i is in this description, and in particular, its type is not specified.