Higher level rigging is all done trough scripts as this gives you finger tip control of exactly how your custom constraints and systems works.
Because it requires a lot of prior knowledge you can't really make tutorials on it since your audience becomes extremely small and all the guys that understand what you're talking about
is probably already riggers or software developers themselves. As >>519407
says it's about following other peoples blogs, reading forum posts where they discuss methods and ideas and so on.
A solid foundation in vector mathematics and a good understanding of how to work with quaternions is the high entry bar that excludes most artists from partaking.
You need to be a programmer/artist cross-class kinda person to venture into advanced rigging techniques.
If you wanna learn something like this, start coding and learn to make various simple constraints from scratch.
Once you know how to write your own position, look-at, IK-chain etc you'll be very liberated in being able to make any custom system you can dream up.