Not public demos on the showfloor.
On the contrary I've played a lot of public demos of MMOs at E3. Warhammer Online, Gaia Online, Hellgate London, Age of Conan, some greek myth themed MMO that never made it to release.
In TES' case however, they tend not to favor E3, and instead hold off the big stuff til Quakecon, but you never know, this isn't BGS this time. If it's in a state where they want people playing it, it'll be playable.