And you’re also quite welcome to work on a SKOS version of FDC. You might want to wait a bit before doing any manual data conversion, though, since as I mention in the FDC documentation, I’m hoping to have a revised version out shortly that will go into a bit more detail than I had time to do for the January 1 release. (It took more time than I expected to verify codes against current usage.) If you’re planning on developing automated conversions, though, feel free to experiment with the plain-text download; I don’t expect the basic text structure to change in the near term, though the text content will.

One thing to keep in mind with decimal classifications like FDC is that trying to put all subjects into a single hierarchy, particularly one constrained by the decimal system, is going to produce some pretty arbitrary relationships in some cases. (Subjects have to go somewhere, and concepts don’t all naturally fall into just 10 divisions.) Broader and narrower relationships are sometimes tenuous in LCSH as it is, and that tendency can increase when everything has to fit into a single decimal hierarchy.

On the subject of the Free-Decimal-Classification, I wonder would you be interested in me helping put together a SKOS version of it? This would give you the added benefit of having URIs for each classification code, and an explicit machine readable serialization.