Proposed resolution:

This wording is relative to N3797.

1. Change [meta.type.synop], header <type_traits> synopsis, as indicated

   namespace std {
     […]
     // 20.10.4.3, type properties:
     […]
     template <class T> struct is_empty;
     template <class T> struct is_polymorphic;
     template <class T> struct is_abstract;
     template <class T> struct is_final;
   
     […]
   }
   

2. Change [meta.unary.prop], Table 49 — Type property predicates, as indicated

   Table 49 — Type property predicates

   Template	Condition	Preconditions
   template <class T> struct is_abstract;	[…]	[…]
   template <class T> struct is_final;	T is a class type marked with the class-virt-specifier final ([class]). [Note: A union is a class type that can be marked with final. — end note]	If T is a class type, T shall be a complete type

3. After [meta.unary.prop] p5 add one further example as indicated:

   [Example:

   // Given:
   struct P final { };
   union U1 { };
   union U2 final { };
   
   // the following assertions hold:
   static_assert(!is_final<int>::value, "Error!");
   static_assert( is_final<P>::value, "Error!");
   static_assert(!is_final<U1>::value, "Error!");
   static_assert( is_final<U2>::value, "Error!");
   

   — end example]