Pop-ups are so last season. The next hip retail concept could be the swap shop. Paris boutique Colette and London’s KK Outlet, a retail space and gallery run by communications agency and publisher KesselsKramer, will showcase a selection of each other’s products from July 5 to 31. KesselsKramer is known for quirky books such as “The Worst Hotel in the World,” about the Hans Brinker Budget Hotel in Amsterdam.