Stealth prequel to Firefly?
I've been thinking about this, and I think there is room for a suggestion that Firefly is an uncredited sequel to this film. Think about it: in Firefly, Earth has been destroyed and humanity has long ago migrated to a new solar system, where they have colonies on numerous planets, presumably using terraforming technology.
In Titan A.E., we see the destruction of Earth, and the remainders of humanity are refugees. At the end, they settle on a new planet, created using terraforming technology.
There are problems, admittedly. Firefly avoids any suggestion that non-human aliens exist in its universe (they are certainly never seen), and there is no interstellar flight either. In Titan A.E., both of these are everywhere. Also, I can't remember whether it is explicitly stated in the Serenity introduction that life on Earth was destroyed by nuclear war between America and China, and that humans reached their new home by means of slower-than-light ships using cryogenic sleep or generations living in a self-contained on-board ecosystem, or whether these things are merely heavily implied. These are not necessarily insurmountable, though. The intervening period between the two time settings is probably several hundred years, plenty of time for the human culture to turn inward and make it clear to aliens that they are not welcome. In Titan A.E., the aliens certainly don't express any particular interest in humanity, beyond sneering at them for not having a home, or much else to trade for. I can quite imagine that such an interstellar culture, when faced with a race who reject them thoroughly, might just shrug their shoulders (or whatever they have instead of shoulders) and leave them be, concluding that they weren't worth the bother. I don't think it is ever stated in Firefly that they can't travel interstellar, they never encounter a reason to do so. As for the rest, well, an industry that can take blond-haired Scouser John Constantine and turn him into a black-haired American played by Keanu Reeves is more than capable of retconning the background of a TV series to make it more simple for a movie audience.
Maybe it's just kinda wishful thinking, but it would be quite fun if it were true...