Hi Dusty,
Collections contain things that do not map nicely to a single taxon name of any (or no) rank. It's not clear to me if this proposal will support those kinds of data or not. A few examples:
Uncertainty: http://arctos.database.museum/guid/KWP:Ento:1703
This is an excellent example of something I have to deal with occassionally, and was going to be part of my never-sent post on dealing with ambiguous identifications. In the context of DwC, my feeling is that this taxon should be represented as "Erebia" in dwc:scientificName, and the two possible species epithets included in dwc:identificationRemarks.
Composite specimens: http://arctos.database.museum/guid/UAM:Herb:12718
This one could be represented as "Bupleurum" for the Individual instance representing the sheet, but then I would be inclined to establish two "child" individuals (semantically related to the "parent" sheet), one each identified to the two different taxa.
I think a lot of data models (including GNUB) treat hybrid formulae as though they are separate "taxa", with the hybrid formula as the name. Although it doesn't seem to be addressed in the DwC documentation, I would put "Canis latrans x Canis lupus familiaris" in dwc:scientificName.
Now....this may be one of those semantics-breaking pseudo-conventions that the RDF'ers will pull their hair out over (along the lines of Bob's post concerning different kinds of aggregations), in which case we should probably have an0other thread on this topic.
Things that aren't taxonomy at all:
http://arctos.database.museum/guid/UAM:ES:3405
Outside the scope of DwC?
Aloha, Rich