What is plug&play? Is it a concept similar to Microsoft's driver system, or is it a startup, or is it a standard for API designers?
I'd say platforms like stackmob which create mobile APIs + wordpress, drupal etc. which make it easy to add an API to those + then platforms like 3scale, mashery etc. which help manage access.
Yep, I guess that's a big part of what's missing still. Mass use of platforms to make it easy for anybody to do this.