In the Batman: Arkham City post-game, you can stumble across some street thugs ruminating on the future of the franchise. They're speculating in-gameworld, of course, but the conversation is blatantly meta. I'm just glad there's a post-game!
The side missions remain, Grand Theft Auto-like, available for your attention after the storyline is over. I probably finished about half of them before credits. After credits, I have cleaned up the rest that are easily accomplishable. Which leaves me staring at 200 unclaimed Riddler trophies, many of which I have no idea how to collect. But that's ok. Given the achievements based around flawless combat combos (that I can never pull off), I wasn't going to Platinum this one anyway.
Some of the side missions are cute little detective bits where Batman has to scan alleyways for clues and track blood trailers and whatnot. I would have liked to see more of those.
A few of them drop serious hints about a sequel, which is a nice tease. Like the thugs say, the inevitable Next Game is a mystery. The creation of Arkham City - essentially a major part of Gotham cordoned off as a massive open air prison - solved a lot of gameplay problems that may not be available a third time. Like, what do you about traffic and innocent bystanders in a game like this, where the main character has the option to beat everyone he sees into unconsciousness?
Then there's the issue of going back to the same villains, again. Every bat-villain of note is in Arkham City. Except Killer Moth, I kid. And at least a third of them were in Arkham Asylum as well.
My fingers are crossed that future DLC will add in-City play for Robin and Nightwing. Although it seems unlikely. They're charging $7 for the ability to play as Robin in challenge maps (IE, not in-game)... how much would they charge to unlock him in the main game, a la the playable Catwoman? $15, assuming you get some Robin-specific missions? And then what if you only buy that, and not the Robin Challenge bundle that's already out there? Maybe $5 to unlock him in freeplay, no bonus missions, but also bundled with the existing $7 pack and priced at $10? I don't know. It's the unwieldy storefront dance and complicated forum explanations that this will require that makes me think they're not doing it.
The game namedrops Huntress and Creeper at one point (I believe during Vicki Vale's hilarious ambush interview with Quincy Sharp back at the church, an easily missable moment). But that seems extra unlikely to expect those two Bat-universe heroes to put in a playable appearance. Still, these guys all have pretty much the same athleticism-based powers...
I did the entire back third of the game, from Freeze-says-make-the-clown-pay to finale, in one night. As the extremely slow credits were rolling, I looked at the clock and was genuinely astonished to see it was 6:30am. Great game.
And come on: the idea that Catwoman and Hush live in the same apartment building? Hilarious.