Hi,
They do rely on the secondary stores being network drives or local systems.
We don't have a remote content store to act as secondary content stores. Such remote replication can be done with RSync, but to have full transactional replication, we'd have to think about writing a remote ContentStore. Effectively, acting as a mapping service for file distribution.
For inbound replication (i.e. a server lazily pulling the content in from a remote location), we could write a store on top of the webdav or web service interfaces.
Regards