I've been to Showest 3 times. Each year the studios are pushing their comic movies harder and harder. My brother saw 04 Punisher several months early there, and I got to see an extended Superman Returns trailer the year before last.
Showest is a very odd thing- its mostly made up of theater owner/manager types who really dont even like movies (or at least arent big fans who geek out over anything). There is some great theater type of food for sampling on the trade floor and if you're lucky they'll debut a trailer or poster for those in attendence. The Bally's/Paris hotels are loaded with celebs for those 3 days because everyone is there accepting an award, promoting a movie, or just popping up as a nice surprise. Jessica Alba and Ioan Grufford posed for a couple pics with me and my brother, which was nice.
Chances are they'll be showing an extended reel of footage introduced by someone from the cast/crew/studio.... there's really no way to know for sure. A couple years ago Singer was supposed to be on hand to intro SR footage but he was 'sick', so Alan Horn did it instead. And everyone is in the dark until they get their itinerary on the first day of the show. Iron Man will certainly have a big presence this year since Robert Downey Jr. is their male star of the year (2 years ago I saw Brandon Routh win male star of tommorow). Its certainly unpredictable, i wouldnt be surprised if they show a lot or even all of the movie.