Proposed resolution:

1. In both [tuple.general]/2 and [tuple.special] change

   template <class Swappable... Types>
   void swap(tuple<Types...>& x, tuple<Types...>& y);
   

2. In [tuple.tuple], class tuple definition and in [tuple.swap], change

   requires Swappable<Types>...void swap(tuple&);
   

3. In [tuple.swap] remove the current requires-clause, which says:

   Requires: Each type in Types shall be Swappable