pyxdg-0.18 has been out for a few weeks. The patches that are used with 0.17 are no longer necessary with 0.18 because the fixes are applied upstream; as far as I can tell, that's the only necessary change to the ebuild.
If the only change to the new version is patches that we already have. The maintainers may choose to not bump it.
There are also some other changes. pyxdg-subprocess.patch hasn't been applied by upstream.
Fixed.