Recently we had an enquiry from a couple in Holland who wanted us to do a home exchange.  Unfortunately, we were not able to consider because we had other plans.  We suggested that they might stay in our home in Canada while we are away visiting relatives and friends on the East coast, with the understanding that at some future time we might stay in their home in The Netherlands.   It's a kind of "I owe you" idea which seems to work quite well  in a home exchange. In other words, home exchanges don't have to be simultaneous.  The same idea works quite well when someone has a second home, a cottage or whatever.