I don't expect anything like the Nepal Uncharted 2 demo but I'm hoping for something like the E3 trailer with some gameplay mixed in
The only reason I think we won't get anything too substantial is because the day of the conference, they would still be a year before an actual release (I think they said Holiday 2015 not fall right?). It seems too far away to have anything too extensive. More character models, sure, more environments and lighting, possible, substantial gameplay (in this case substantial is like more than 15 seconds) could come back to bite them in the ass. Look at how people crucify the order from the gameplay they have shown and that was from May.