Actually, the method call will change when we are using split. It will need to change to create_item (which delegates to create_and_save_xmodule if the modulestore is mongo).

I added a check of hasattr(self.system.modulestore, 'create_and_save_xmodule') to the assert. This will fail with mixed, and the code will need to be updated (signature of create_item is slightly different too). I don't think there is any choice at the moment.