Actually, I meant that Tai Lung should return only to work alongside the heroes, even if reluctantly or not. Simply put, in the first movie, Tai Lung's motivation was the Dragon Scroll, nothing more and nothing less, and we saw the breakdown he had when he found out it was blank. Thus, he should have no more reason to seek the scroll. Though, considering how proud he is, defeating Po in combat could count as revenge and be a new motivation for him. But having him return as a villain would get tedious and boring, since we know Po will always win in the end due to the rule of children's movies.
Nevertheless, the plot for the new movie states that the new villain has an ultra powerful weapon, and also states that Po must confront his past. Of course, this could mean he gets to learn about his birth parents (cause, you know, that dad of his...) but it could also mean a need to confront Tai Lung in order to try to convince him to help out in defeating this new threat, seeing as how Tai Lung's powerful enough to defeat all the Furious Five and even Shifu, so his strength would be needed. That and having him around could cause all sorts of comedic situations between him and the other characters, especially if he has to spend time and fight alongside Po.
I sure do hope that that's what it means, since Tai Lung has the most potential out of any of the characters in KFP, in my opinion. Sadly, the series is still titled Kung Fu Panda, not Kung Fu Snow Leopard, so it sorta worries me that a character of such potential could be wasted. That and it would be a disappointment, as well as a huge cop-out by the makers of the film, if we never get an explanation as to what the heck happened to Tai Lung after the Wuxi Finger Hold.