first of all, thanks for an unbelievable resource for facial rigging, this once opened my eyes on how facial setup could really be done! still using quite a lot of concepts from your book, it was extremely helpful.
i would love to see all the modeling-part stripped; not many riggers will model themselves these days; instead, need more focus on : 1. major topology requirements; 2. areas that must be doublechecked when preparing for rigging -e.g., my list would start with checking lip corners/inner shape to make sure it’s rounded, not flat, and eyelid topology - is closing the eye possible? also, more general guidelines for tooth size/position, topology between eyebrows, summary of a must-have topology for creases of smile fold, squint wrinkles, etc… should be like a checklist for a modeler before submitting a model/ rigger upon receiving it and requesting for changes.
what we find in our studio most challenging is making lips and eyes believable - the rest of the face doesn’t even matter if those do not work well.
lips still lack some fake for softiness effect (it never feels like upper lip is touching lower lip). animators play quite a lot with second-layer controls (face points) to adjust them in closeups.
our fleshy eye setup is still pretty mechanic, would like to see some more ideas on that. we use a complicated blend of forward-up-down-inward-outward shapes for each stage of the eye - neutral, neutral+squint, closed, closed+squint, wide open. Controlling long eyelashes is an issue too (making them look good when eyes are closed and not penetrate eyebrow mass with eyes wide open/view direction up). we also had to throw away upper eyelid/lower eyelid concept and work with eye open-eye closed as a base, adding overlay of upper/lower lid: this allowed achieving easier watertight blinks/closed eyes at any eye pose, even with a squint blended in.
other “latest fashion” tricks would be nice - switching between closed mouth/open mouth when jaw is moving (chewing vs talking); better sticky lips solution (soft mod one just doesn’t cut it). “face points” is mandatory these days as well; two-layer face points system would even be greater (smaller detail face points act on top of bigger detail face points).
Good luck with our book, i’m definitely buying that one!