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Also, I'm mystified as to why this is even of interest, when in Poser we have not just virtual displacement mapping, but REAL displacement mapping.

Sorry, man, I'd have to disagree with that.
"REAL" displacement mapping involves micro-poly displacement of a subdivided model; the displacement map imitates huge displacements of a polygon model in the millions, while using only thousands, in subpatch, at render time.
Poser can't subdivide a mesh, at render time or at any other time. Yet.
Is one of my UberPoser wishes. ;-)