A Btrfs stream with the send/receive support can be used for re-constructing sent sub-volumes/snapshots. Alexander Block wrote in his kernel patch thread, "The main usage for send/receive in the future will probably be backups." But for now, the support is still considered experimental so he says, "If you use it for backups, you're taking big risks and may end up with unusable backups."
The send support to Btrfs in the kernel adds around 5,000 lines of new code. The Btrfs user-space (btrfs-progs) also requires updates, which can be found in this other mailing list thread.
Chris Mason, the Btrfs creator and continued maintainer at his new job, said "Just awesome. I'm playing with this now." This work will be part of Btrfs 0.21.