I would like to see in the book the following:

1) Synchronous vs Asynchronous API design discussed
2) For folks to refer back to particular API semantics or patterns or recipe, put it in "effective" format ala Scott Meyers "Effective C++" or Joshua Bloch's "Effective Java". This is to prevent readers from reading "lots of leaves" along the way and lose sight of the context or gist of the topic.