AvatarSpirit.net recently interveiwed Gene Luen Yang. In the interview he talks about working in the comic book industry and his experience writing for The Promise Part 1. He also discusses some of the events that take place in the graphic novel and hints at things to come in the futher installments of the trilogy. Some of the information he reveales is that Azula and Iroh will make future appearances as well as Suki who "we'll definitely be seeing more [of] especially in the third volume."
As for the mystery surrounding Ursa's disapearance, Gene remarks "that was the first question I asked when I got on the phone with Mike and Bryan! Ultimately, what Ursa's absence means to Zuko is more important than what actually happened to her. Mike and Bryan pointed that out to me. They're right, of course. But that's not to say we won't eventually find out the specifics." When he was asked about the possiblity of future graphic novels/comics beyond The Promise Trilogy to further tie A:TLA and Legend of Korra together, Gene notes that he hasn't heard any new yet but "the time span that The Promise covers is so short -- just a fraction of the seventy years between the two series -- that there's plenty of room from more great stories."
To read the full interveiw click here