On WiX 3.6.3005 it's not possible to define RemotePayload element for a Payload element.
Project does not compile when removing the SourceFile attribute of the Payload element:
error CNDL0107: Schema validation failed with the following error at line ..., column ...: The required attribute 'SourceFile' is missing.
Keeping SourceFile attribute in Payload results in:
error CNDL0372: The Payload element cannot have a child element 'RemotePayload' when attribute 'SourceFile' is set.