I was hoping they would have Dark Sun material being added this update because I am starting a new campaign next weekend. I can wait on Essentials, but my group have roughly created their Dark Sun characters and I would hate to have to tweak with the Compendium to get things right, and then untweak it when they are officially added.
But thats just my personal story, so if it comes out in time, it would be great. If not, I'll just tweak it.