I stress "could" above, because I'm a little surprised it hasn't happened yet. There was movement in that direction at least as far back as 2005 [http://dcpapers.dublincore.org/ojs/pubs/article/viewFile/808/804], and I heard the idea discussed back at the Montpellier VoCamp. I don't know if lack of progress here is because of lack of funding, or because the problem is a lot harder that it at first appears. I'd love to see a concerted effort in this direction, starting modestly, focusing on a small taxonomic group for which there is already a lot of SDD instance data. (This would, IMHO, make a strong funding proposal.)
It is lack of funding and person resources. The SDD working group did realize as far back as ca. 2000 (Noel Cross was the first to point that out to me) that RDF is a match for SDD. However, it was really difficult to grasp the implications at that time, we found rather than making progress on the subject domain (build on DELTA and slightly modernize it) we were hitting a wall. So we purposely decided to stay closer to object oriented modeling and map this to xml schema. It took us 5 years to gather the necessary competence in xml schema to finalize SDD, and when at the end of that period the leader of tdwg made the decision that all needs to be re-done in RDF we were exhausted and in fact almost all SDD core members were out of funding for identification or descriptive work.
I welcome any intitiative to create an OWL-compatible form of the core concepts of SDD - with or without my participation.
Gregor