This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
The grammar for type-id in 11.3 [class.name] paragraph 1 has two problems. First, the fact that we allow an abstract-pack-declarator makes some uses of type-id (template arguments, alignment specifiers, exception-specifications) ambiguous: T... could be parsed either as a type-id, including the ellipsis, or as the type-id T with a following ellipsis. There does not appear to be any rule to disambiguate these parses.
The other problem is that we do not allow parentheses in an abstract-pack-declarator, which makes
template<typename...Ts> void f(Ts (&...));
ill-formed because (&...)() is not an abstract-pack-declarator. There is implementation variance on this point.