Comment # 7 on bug 1174067 from Thomas Schmidt

I would not recommend to have "zypper migration" in it's current implementation
as a documented way to migrate openSUSE Leap to the next version. 
The implemented usecase is only migration Leap to SLES. 

I could make sense to add special handling to the "zypper migration" plugin to
handle the openSUSE Leap upgrade case by just replacing the local repos and
running "zypper dup". This would be a feature request to be evaluated by
openSUSE. 

@Ulrich: Before running "zypper dup", you need to change your local
repositories to point to the Leap version you want to upgrade to.