Aspera did the chunking and encryption for you, and it looked and acted like SFTP.

The cost of leaking data was/is catastrophic (as in company ending) So paying a bit of money to guarantee that your data was being sent to the right place (point to point) and couldn't leak was a worthwhile tradeoff.

For Point to point transfer torrenting is a lot higher overhead than you want. plus most clients have an anti-leaching setting, so you'd need not only a custom client, but a custom protocol as well.

The idea is sound though, have an index file with and then a list of chunks to pull over multiple TCP connections.