Chris Mason, now employed by Facebook where they're beginning to use Btrfs, sent in the first batch of changes for the Linux 3.15 kernel merge window. There doesn't appear to be any major Btrfs features for this next kernel revision but is mostly focused around a ton of fixes.
There's many bug and performance fixes that landed while some corruption fixes and other patches will land later in the 3.15 merge window. The Btrfs code was also changed to avoid using its own async threads in favor of regular kernel work-queues, in hopes of using more generic code, but it might affect the file-system's performance.
There's over 100 commits affecting thousands of lines of Btrfs kernel code with this initial pull request. Those wanting to find out more about the queued up fixes for Linux 3.15 can find the kernel pull request with all of the commits. Hard drive and solid-state drive benchmarks of the popular Linux file-systems on 3.15 will come once past the merge window and development has begun to calm down and stabilize. Those interested in 3.14 stable can see our earlier SSD file-system numbers from a few weeks back.