Does Merkel's coalition spat prefigure a change in the German party system?

The alliance between Angela Merkel's CDU and their Bavarian sister party, the CSU, has come under strain over the German government's immigration policies. Ben Margulies writes that while most of the coverage of the CDU-CSU dispute has focused on what it means for Merkel's government, it provides some insights into the potential future trajectory of the German party system.