Currently when a node is retrieved, the source nid is checked to determine whether or not the node has been retrieved before and insert or update accordingly.

It would be useful to have an option to instead use a UUID created by the UUID module.
Alternately some other unique identifier could be used if you didn't want to use the uuid module.

This would mean you could be retrieving from multiple sites without clashing.

This is related to #711754: conversion to a Clients plugin, which would allow retrieving from multiple sites.