Right, that is exactly what I want to do: to back up the data on my computer into an untrusted remote device. To do that, I need to first bootstrap the system. That is, I have to do the initial backup. When the amount of data to be backed up is large (e.g., several TBs), it makes no sense to do the initial backup over the network. It would take a lifetime. Instead, I would like to do it locally and copy it to the remote machine using, for example, an external USD drive.
Note that this type of bootstrap functionality is supported by regular backup systems. For example, IDrive offers the IDrive Express service, which is described as follows: "Quick backup and retrieval of your data up to 3 TB in less than a week via physical storage shipment, ensuring no bandwidth usage". Having bittorrent sync support this type of offline bootstrap would be fantastic because this functionality is the only piece missing to fully support untrusted nodes.
So, why is having two versions of the same folder (one with read/write rights and the other encrypted) on the same device not supported? Is this a limitation in the bittorrent protocol (e.g., the way folders and devices are identified on the wire), or is it a limitation in the client (i.e., because it checks that a given folder can exist only once)? If is is the latter one, it would be easy to fix it, I guess.
Thanks!