It seems like the possibilities of Uldum, in Southern Tanaris, have sparked the imagination of lore fans and adventurers ever since the first person turned in the Discs of Norgannon out of Uldaman. The wealth of Information we recieve from the quest about the intentions of the Titans (those whom the disc calls "The Creators") and the origin of not only the Dwarves, but possibly every sentient race on Azeroth, is tremendous, and Uldum only promises to bring more of it, revealing incredible secrets about the origin of life on this and perhaps other worlds.
Unfortunately, since we apparently need the Plates of Uldum to access it, it remains closed for now, and we're stuck with speculation about what could lurk in its halls. However, today, Drysc commented on the possibilities himself in a forum thread. While all he really confirmed is that they DO plan to open it at some point, it's still more than enough of a bone to get the old speculation machine turning.
Warning: Spoilers ahead!