If they're showing the conference in movie theatres, I'm guessing Sony must have some big reveals planned. Otherwise... what's the point? Seems like a tremendous waste of money and time otherwise. However, E3 conferences from Sony have been pretty poor over the years so I'm not sure what to expect.
I think the last good conf was in 2009. Every other year it has been terrible. E3 2012 was saved by one of the best demo's I have seen at E3 with TLOU.