In terms of what wbinvd does, it makes no sense to execute that instruction at that point. Write back? To where? Many memory controllers will hang if you try to use them before they're configured (personal experience). I believe that set of 16-bit instructions was written by me for linuxbios ca. 2000, when my understanding of these details was tenuous, so the wbinvd at that point was probably my mistake, which Eric corrected in 2004. I tend to expect that's why there was not much discussion in 2004 -- on the face of it, a wbinvd at that point just seems wrong.
As for the 2012 discussion, I'd forgotten it completely.
I think the most we could do is a config option to enable this, and it seems like a bad idea in any event unless we really care about the z250p. The wbinvd at the POR vector seems like a hack for a buggy chipset.
But it's certainly interesting.
ron