Just to articulate that idea further, here's an overview in written form. The idea is to take your blendshape performance and Ziva-fy it to get some extra sim goodies.
If you can do a two-phase sim that does something like the following you should start to see some results.
Fit a skull, mandible, deep facial muscles (temporalis, masseter), some neck muscles, to your current head.
Make another layer of 'skin' that's based on the outer skin, but projected onto the objects detailed above.
Ideally the borders of the two meshes would line up exactly to the vertex. So the eyelids, lips, neck vertices would be concurrent for the two layers.
Sim Pass 1
The first pass is to articulate the inner layer moving. You could use tissue to do this. Take a copy of the inner/outer layer, combine them, convert to tissue.
Take the animated outer layer (the blendshape performance) convert it to a Ziva bone, and attach your tissue to it. Wrap the inner layer to the tissue, export the wrapped inner layer.
In this pass you could also have the tissue collide with the underlying objects (skull, deep muscles etc)
Sim Pass 2
This would be a separate scene to the first pass, but they'd look similar.
Import the animated inner layer from the previous pass.
Again, have a volume as defined by the combined/merged inner and outer layer, convert to tissue.
Make the animated inner layer a Ziva bone, and attach your tissue to it.
Take your outer layer (not animated, just a copy) and convert it to ziva cloth.
Attach it to the tissue. Make sure collisions are turned off on the cloth, as you don't need the cloth to collide.
There's lots of options to try in the second sim pass. You can make the animated outer layer a ziva bone as well, and attach the tissue (or the cloth) to it. You can have many different attachments and play with the envelopes of those attachments (key them, automatically maybe based on blendshape attrs) Because sometimes you'll want the lip lines to match exactly and other times you want the sim to be free.
Think you'd have to go pretty highres to see microstructure stuff, but could be worth a shot? hi res cloth and or tissue sim?