Ontology Mapping, Ineffable Subjects and Blank Nodes

In this thread on SWAD forum, Alistair Miles and Dan Brickley re-activate an old issue : How do I express that resource X in representation scheme A (e.g. a SKOS concept scheme) and resource Y in representation scheme B (e.g. an OWL ontology) are somehow representations of the same (----) . After suggesting a suboptimal Topic Map solution I suddenly yesterday came out with the idea that in RDF, blank nodes could be a killer solution. Actually one can use blank nodes to aggregate various representations of whatever, keeping agnostic on what this whatever is. Using blank nodes to represent "ineffable subjects" is cool, since nobody is able to say anything directly about them (asserting name, type or any other property), since they have no URI. Put it together with recent debate on ISO SC34 mailing list about subject locators, and consider this provocative conclusion : RDF blank nodes are better than TM topics at representing subjects, since, and this is my last thought, subjects have no identity, only representations have one. Subjects have no identity, read no type, no property at all. Resources have identity (URIs), so the best attempt to indicate a subject is to gather various resources in a blank node, as so many fingers pointing towards the moon.
Remember in the Topic Maps book, I wrote about an empty subject indicator ...