Quote - I understand that what available in the plugin is roughly that of a subset of Poser 5's nodes... sound right to you?

That's about right

Quote - Do you think it's even worth trying to emulate the shaders Poser users enjoy?

For anything that doesn't use some of the more exotic nodes, then recreating most of what's left should be possible.

IIRC, Eilir use RSL (see -> http://en.wikipedia.org/wiki/RenderMan_Interface_Specification) so it maybe possible to do some things that Poser can't (and new nodes get built for the effects).