Next time when Azula betrays him (I think she will eventually, if not right away), he'll be ready for it. He could deflect her lightning like Iroh taught him to. Bitter Work would make sense again in that case. It could be that he's merely "testing the waters" to see if turning against his family is truly the right decision for him. And by the time the betrayal happens, he'll likely be deep inside the Fire Nation's plot.
If that's how the season goes, then it would parallel Aang's journey again. Apparently Aang and co. will be going into the Fire Nation, and that makes even more sense now that the Earth Kingdom has fallen. They'll have nowhere to go but into enemy territory. In this way, both Aang and Zuko can work against the Fire Nation from the inside.
There's also the issue of how Aang will learn Firebending. My hope is still that Iroh will escape, or Zuko would set him free in some way. Jeong Jeong could also be a candidate for Aang's master, but Iroh and Jeong Jeong are both enemies of the Fire Nation so at this point I think it'd be just as likely for either of them.
I think that Toph's metalbending could be important too, especially if they gather up some resisting Earthbenders (Haru and his father?) to try to learn it as well. They could probably take out some Fire Navy ships that way, and gathering as many allies as they can would be crucial at this stage, including the Water Tribes and hopefully the Kyoshi warriors. So while the entire season would be focused on Fire, the elements of Water and Earth would still be represented.
Then there's the issue of the solar eclipse. Azula knows about it now so a sneak attack is out of the question. That doesn't mean Aang and co. can't take advantage of it while they're in the Fire Nation, though. Also, if Azula cannot firebend anymore and has to fight Zuko, who would be at a greater advantage? Zuko has some great swordfighting skills. Does Azula have anything else?
Back to Zuko, this could also offer him an opportunity to find out more about his mother. Whether he finds her or not....I don't know. I'm just speculating.
I also noticed some repeated themes between The Avatar State and The Crossroads of Destiny. (1)In The Avatar State, Katara is given her holy water. In the finale, she finally uses it on Aang. (2)Aang attempts to master the Avatar state, but is unable to, and it's revealed to him that being killed while in the Avatar state can end the Avatar cycle permanently. In the finale, he's finally able to master the Avatar state, and is nearly killed in the process. (3)In The Avatar State, Zuko decides to trust Azula despite Iroh's warnings. In the finale, he does so again, but this time he's gained some wisdom and insight. This makes me think that the creators did put some thought into the twists of the finale, possibly from the beginning of the season.
Now I'm just hoping that I'm right.
EDIT: Also, I clearly need to rewatch all of Season 2. Most episodes I've only seen once, with the exception of The Blind Bandit, which I probably watched 5-6 times.
EDIT 2: It needed to be iconed. :D