Thiagi and Piskurich speed up the task by making the learning task more open-ended and constructivist in approach. Therefore, the design of instruction is often blended with the development and delivery of instruction. Most IDs don't often get to deliver (unless it's eLearning) and even then, they rarely have control over the environment in which the learning occurs. Most instructors may have developed curriculum, but generally are often more likely to be subject-matter experts (SMEs) than curriculum developers.
I would like more opportunity to try out Rapid ISD approach and plan to do so in my upcoming projects as much as possible.