It'll probably be supported, but more likely in 2.1 than 2.0. The XZ format is apparently kind of an overengineered mess and would take some work to support.
(Also, what happened to the other formats that adopted the format while it was still called LZMA-utils, like RPM 5 and XAR? Is the finished XZ format still compatible with those files? Or is there some intermediate version that I'd need to support too?)