Thanks for this! I'm a designer who has worked hacking several game systems and studied countless more, and after my first look at this compendium, it's an excellent read! The first few sections I read all cover various systems used for particular aspects in tabletop rpg design, old and new. And i really appreciate the organization into short, concise sections for easier parsing. Will provide a more detailed review when I get time to peruse deeper (in particular, to see what ideas you put forth on what hasn't quite been done yet).
Cheers!