It's been over a year since I last gave an update on this. I streamlined the shader further, eliminating stuff that did not have visible benefits. Setting up nodes to easily change lip color etc. Lips look much better now. I also optimized colors for an ACES workflow.
I'm pretty confident that with DAZ textures alone it won't get much better, so I call this finished as far as quality is concerned. Now I want to set up a few simple Xpresso controls for tan, lip color, skin reflectivity etc. Hope it won't take another year ￼
P.S. when this is finished I will create a vface-optimized version.