You should be able to re-use the existing rigging. I've always maintained the low-poly (~10k) and "high"-poly (~40k) versions in parallel. The only bit that was really painful were the JCMs. I can automatically transfer normal morphs onto a subdivided mesh, but that doesn't quite work with JCMs (I forgot why exactly).

If it's the WM version, and just transferring the base mesh and morphs, I think the only practical problem would be that my current Scala code for doing the subdivision is terribly slow and clunky, and it uses up a lot of memory. So it's either finding an unused, reasonably high-powered computer and let it run for a few nights, or else bringing my Python code "up to speed".

-- I'm not mad at you, just Westphalian.