Actually, people should be aware that in addition to the reasons you cite for providing a migration path, resellers are still selling their Xadow1 boards. As the naming is pretty bad or is getting transmitted badly (from what I read I was not expecting the XADOW to be version 2, but rather the sensor to be version 2!), there will also be other customers than just me still buying Xadow1 boards for some while with a view of using them with the Rephone kit.
So a migration path would keep people like me happier than I am right now.