Per Robert Buchholz on the XSPF developers mailing list, we are now supported by Gentoo out of the box:

libspiff is part of the official Gentoo tree for some weeks, living in an overlay maintained by myself for some time before. Also, PEAR-File_XSPF is part of Gentoo already.

For an average PC user this is completely meaningless, but as an internet developer and a product of unix culture, I feel great about having played a part in it: our work is being absorbed into the background set of computing resources.