Did you notice that P6 has 7 tabs at the top. With a bit of imagination some line up with the reasons to get P7 so far.

Content: (reason #1 new content)
Face: (reason #2 lip sync)
Pose: (reason #3 undo)
Material: (reason #4 better renderer)

Still to come:
Setup
Cloth
Hair

Setup has got to be the rigging improvements that everyone has been clamouring for.
Cloth must be the answer to Daz Optiwhatsit.

I think I am onto something here. In the preview pictures they were very careful to cut off any clothes and strandbased hair in rendered state, although some figures had strand hair in preview mode.

Hmm. They will keep the killer feature until last. Which one will it be?