We are implementing a feature like this currently. I takes some time since it's not very easy to handle all the different file pieces efficiently for large files. We also have to adjust some of the very old and terrible Phex/Furi code to integrate it well.
Currently we are only two developers. This makes it difficult to bring new features, cleanup code, and fix bugs in short time. So anybody who likes to help improving things here or there is welcome.

The next major release v0.7 might contain this swarming download ability. But don't ask me how long it takes until it's ready ;-)

Gregor