Last time i predicted around what Avengers did, people called me crazy for saying it would beat The Dark Knight Rises in the box office and pass the billion mark by a good margin, who's laughing now?
I predict 1.2 billion to 2 billion, i don't think it will make as much as Cameron's films but it may come closer, who knows, but i think it will just do around the same ammount of money Avengers did, Superhero films aren't everyone's cup of tea yet, so it's not as broad as Titanic or Avatar, but if the fandom keeps expanding, then it has a good chance of getting to the 2 billion club.