To show what exactly? Mists is coming out now, so at best they'd just have 5.1 stuff to show. Diablo III just came out, so all they'd show is patch stuff and possibly a hint of expansion stuff. SC2 would be the biggest thing since HotS isn't out yet, but it's in beta already and has been shown at the past two Blizzcons already. We know they're not ready to even have a teaser for Titan until next year, and I'm not sure if there was another project brewing or not, but that wouldn't be near ready to be shown either. Blizzcon is used to announce/promote new stuff more than anything else, and there wouldn't be anything new.
Expect some big stuff next year though - new WoW expansion, DIII Expansion, HotS should be out by then, so patch stuff/tournaments for that, and finally (hopefully) at least some news on Titan.