I'll begin by attempting to convey my understanding of Peikoff's DIM Hypothesis. To begin with DIM is an acronym made up of the three fundamental concepts in Dr. Peikoff's hypothesis. D stands for Disintegration, I for Integration, and M for Misintegration. From the description of the recent course:
The course is based on Dr. Peikoff's book-in-progress, The DIM Hypothesis, in which he looks at the role of integration in the culture and in practical life. As Dr. Peikoff recently explained: "my thesis is that the dominant trends in every key area can be defined by their leaders' policy toward integration: they are against it (Disintegration, D); they are for it, if it conforms to reality (Integration, I); they are for it, regardless of its relation to reality (Misintegration, M)."
A further word on the term "Integration" as used in the context of Objectivism. In her book Introduction to Objectivist Epistemology Ayn Rand discusses the fundamental processes of consciousness thus:
Consciousness, as a state of awareness, is not a passive state, but an active process that consists of two essentials: differentiation and integration.
Specifically, in terms of concepts:
A concept is a mental integration of two or more units which are isolated according to a specific characteristic(s) and united by a specific definition. [italics added]
Thus integration is fundamental to the nature of concepts. Dr. Peikoff argues that integration is not only fundamental to the nature of concepts but in fact a given intellectual sphere's attitude toward integration allows for a deeper understanding of that intellectual sphere's views on any number of issues. It turns out that regardless of the intellectual area, if its atttitude to integration is similar to another movement's then certain things will be the same about the two movements.
Integration is taken to mean that in a given intellectual area, the leaders of an intellectual movement identify the relevant factors in reality and relate and thus integrate them via a logical method. This method yields principles of understanding and action as appropriate and the movement is thus a systematic, integrated, reality-based approach.
One alternative to this is termed by Dr. Peikoff Misintegration. Misintegration amounts to attempting to do integration but doing it wrong. Here the leaders of an intellectual movement rely on unreal elements as the foundations of their views and attempt to combine them into a systematic view of the world. This approach also yields certain principles of understanding and action.
Finally, there is Disintegration. Here practitioners explicitly reject attempts at integration as misguided and wrong. The foundation of their views tends be reality based but is not limited to such elements since no attempt is made to systematize the views. This view is opposed to any principles of understanding or action.