Regarding \Threshold Concepts,\ you may find the work of J. van Merrienboer of interest. I have found the notion of Threshold Concept can be thought of as an abstraction of part of Merrienboer’s model of complex skills. He addresses models of not only the static knowledge of complex skills including mental models of related knowledge, but also the dynamic aspects (cognitive load). Link: http://www.ou.nl/Docs/Expertise/OTEC/Publicaties/jeroen van merrienboer/Merrienboer-Blueprints_for_Complex_Learning_2002.pdf

Thank you for addressing Threshold Concepts.