Most of the online backup businesses are not going to be interested in trying to do that unless you're paying a fair bit of money. Carbonite's default plan looks like they slow you down after 200GB. That's not much NAS data. On the other hand, if you have a FreeNAS with just 4TB of space, how fast are you going to be able to upload that anyways? If you have 10Mbps upstream Internet service, you can push maybe 1MByte/sec if you're lucky, and don't need the pipe for anything else, but that's like two MONTHS to submit your initial snapshot.
The realities of Internet speed vs NAS storage space favor other solutions.
