According to Forbes.com contributor Scott Mendelson, "there is a pretty decent chance that not a single film will gross [a billion] in 2013."
With this said, he does acknowledge the possibility for surprise, pointing to Star Trek into Darkness, Iron Man 3, Man of Steel and Pacific Rim as possible candidates for breaking a billion:
"There is the possibility for surprise and the unexpected breakout. Star Trek made just $395 million worldwide in 2009, but it’s certainly possible that the 3D/IMAX-enhanced Star Trek into Darkness could ‘pull a Dark Knight’ and capitalize in the original’s good will and massively outperform its predecessor (Batman Begins earned just $375 million back in 2005). But that’s not a guarantee.Iron Man 3 could build on the success of The Avengers and earn $1 billion the third time around, again enhanced by 3D and IMAX, but the previous two films topped out at $585 million and $623 million respectively, so that’s an awfully big jump to presume. Man of Steel is no guarantee, as Superman Returns earned $391 million back in 2006 and it’s partially a question of whether or not the Zack Snyder-helmed/Christopher Nolan-produced epic can deliver an iconic Superman film and/or whether the world still needs a Superman film. Pacific Rim is the major wildcard of the summer, an original entry that is gaining massive buzz among the geek set but. But even with that whole 3D boost thingy going for it, I’d argue that how well Guillermo Del Toro’s monsters vs. robots epic does in July depends on how good or bad the summer slate up to that point is (I’ll expand on that in a later essay)."
Mendelson does not see Thor: The Dark World as breaking $1 billion, arguing that the movie "will surely get a post-Avengers boost, but going from $449 million to $1 billion without a major selling point (like a marquee villain played by a major star) is arguably impossible."