^^I can't see Azulon murdering his father. Why would he wait until he was old to do it? If he was power hungry like Ozai, he would've done it much earlier, like Ozai did. Obviously something happened, but I don't think that Azulon had anything to do with it. He seemed to be a pretty traditional guy, so I believe he would've waited his turn.
I do hope we get to see that part of the story, though. It'd be interesting to see what did Sozin in, other that old age.
I'm sure someone already has mentioned this, but the red dragon/blue dragon dream now has a completely new context. The blue dragon represented not only Azula but Zuko's lineage on Sozin's side. Conversely, the red dragon represents not only Iroh but Zuko's lineage on Roku's side. Good and evil are represented within Zuko's dream (and Zuko himself) through his two great-grandfathers and their history.
More than that, though, the idea of "friendships lasting more than one lifetime" applies to Zuko's relationship with Aang. Aang is the living embodiment (literally) of Roku. On the flip side of this, however, is Azula. She is the descendant of both Roku and Sozin, but has clearly taken after Sozin. He is a fascinating character to me symbolically and in the end he has (IMO) the most difficult choice to make.
Sorry for any rambling....
"I will never, ever, turn my back on people who need me"