You know, I really hope that it doesn't play out like that, and that it comes AFTER the tv series. Although I'm DYING to know what Bron and Shorty's initial reaction to having a Sharptooth in the valley AND him being friends with Littlefoot, I think that aspect could be kind of a point that's developed in the 14th movie, but not the subject of the movie itself.
If you think about it, it would make a lot more sense to have it played out after the Big Longneck Test and the tv series, mostly because you can get so much more development to work out characters and tell the story of how Bron and Shorty first came to the Valley through those characters and the adventures that they'll go on and the things that they'll go through, rather than being tied down to "Okay, so we need to make X and X happen to reach to the point that we've already established". To a certain extreme, if that were the case then it could be considered a midquel.
One thing that I really adore about the series is that it knows how to create and write characters. Stories and plots? Maybe not, but they do know what they're doing when it comes to Littlefoot and the gang (We've had 13 movies and 26 episodes, damn it). Adding Shorty to the mix (Which I pray to GOD that they do) can help serve that purpose of, "Well, you know how when we first came to the Great Valley that..." story that many of us (presumably) want. Having him join the gang to look for his and Littlefoot's dad with Chomper and Ruby too, can definitely bring up some good conversation about this kind of strange relationship.
As we saw in the Big Longneck Test, Shorty has a big problem with how Chomper eats, but doesn't seem to mind the little guy all that much. But, can you really blame him? On the other side of it, Chomper seemed to, for lack of a better term, almost idolize Shorty when he lied about taking the test himself, and was the first one to jump at the chance of going to the Great Stone Walkover with Shorty leading the way. It could be Chomper's goal of trying to "assimilate into the herd", but it could also be something of a "Well, this is Littlefoot's brother, so he's probably pretty cool!" mindset that he could very well have. Assuming that the 14th movie will include tv canon, development between Shorty and Chomper should prove interesting. It could also prove how that initial reaction was. Who knows? Maybe we'll get some flashbacks.
We don't need to know what exactly happened before the Big Longneck test, and we don't need that to be a full 1 hour and 20 minutes. That story can be worked into the film, but I definitely don't think it's a good idea to make it just about that. Having a separate adventure looking for Bron is more than fine with me.
