Our goal in 9.4 was two-fold:
1) deliver a set of tools for building complete map books Many people express a need for mulitple layouts because they want to achieve one of those two things. There are also other reasons people want multiple layouts. The 9.4 beta period will be very important for us, as we need to understand which problems 9.4 has actually solved, and which workflows still need solutions.
2) provide an automated way to update layouts, data frames, and map documents
I think our future plans regarding multiple layouts will should be made with unfulfilled user requirements in mind. For now, our solution is what you see in 9.4, focused on satisifying the above two requirements. In the future, we can consider full multiple layouts but should do so with a set real world goals. It would be great for us if you could provide additional details about multiple layout workflows. I think that some needs could be covered with the new 9.4 python scripting experience. Other requirements should go on ESRI's list for a future release.