Having that code licensed under the GPL is especially useful: any code which is useful in its current form can be pulled quickly into Linux. And, even when the code itself cannot be used, the ideas that it embodies can be borrowed without fear. And that is exactly what HP was hoping to encourage with this release:
In case its not clear, this is a GPLv2 technology release, not an actual port to Linux. We're hoping that the code and documentation will be helpful in the development of new file systems for Linux that will provide similar capabilities, and perhaps used to make tweaks to existing file systems.
And that would appear to be likely to happen. Over time, the best ideas and experience from AdvFS should find their way into the filesystems supported by Linux, even if AdvFS, itself, never becomes one of those filesystems. So HP has made a significant contribution to the kernel development process, one which will probably never show up in the changeset counts and other easily-obtained metrics.
(Those interested in learning more about AdvFS would be well advised to grab the documentation tarball from the AdvFS sourceforge page. The "Hitchhiker's guide" is a good starting place, though, at 229 pages, it's not for hitchhikers who prefer to travel light.)