well, here it is! The SAP TM Enhancement Guide is now available here at the SAP Community Network. I just received the link to my document yesterday. Here’s the Link of the first version I’ve published in the SCN: https://scn.sap.com/docs/DOC-32985
I have already plans to add further content to the document as well as to rework it at the one or the other section. Hope the content of this document version helps you already to get started with your SAP TM Enhancement Project. I’ll keep the document up-to-date and let you know when a newer version of it is available.