Essay time!

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Yes, Chomper is going to be in the TV series. It was confirmed in one of the first announcements of the TV series. It did say that Littlefoot, Cera, Ducky, Petrie, Spike and Chomper would be having new never before seen adventures.
At this point, it will be difficult to say just how often Chomper will be included in the series, but he is another case where I hope he doesn't become a permanent member of the Gang, for a number of reasons. First of all, being a sharptooth, he would not generally be welcome in the Great Valley. Second of all, if he was there, chances are his parents would also be there. I fail to see a logical way to move full-grown sharpteeth into the Great Valley permanently.
Another possibility is that Chomper's parents are killed, or Chomper is seperated from them for some reason. I am then curious as to how Chomper would make it all the way to the Great Valley without his parents. Not to mention, I doubt Chomper knows the way to the Great Valley (unless the Gang told him in detail how they got to his island, when they met him again in LBT 5, in a scene the audience didn't see).
As long as
1) They don't make Chomper a permanent member of the Gang, in most or all episodes, and
2) They don't magically transport anyone anywhere,
I'll be happy.
Having a very close relationship with Ali would definitely alter Littlefoot's relationship to the others as well. If there was a kind of romance Ali couldn't simply be treated just like any other character. I have very often laid out my impression of a "sandbox-love" between Littlefoot and Ali.
I see where you're coming from, however I still can't believe in a relationship between Littlefoot and Ali as being as strong as the relationships between Littlefoot and Cera, Ducky, Petrie, and Spike. I get this impression for a few reasons, such as:
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Littlefoot and the rest of the Gang are often thinking of each other. For example, when Spike leaves, the Gang feels hurt and Ducky especially misses him very much. The Gang is concerned about him until the very end, when Spike's herd stumbles across the Great Valley dinosaurs' hot springs. I will admit this is not necessarily a fair arguement because Ali leaves at the very end of LBT 4, leaving no time for anyone to feel her "loss". If we take a look into the series, however, Ali is Never again mentioned by any members of the Gang, including Littlefoot. That makes me wonder just how close they really are to Ali. They didn't know her as well as they know each other. I'm sure Littlefoot would like to see her again, but there is no evidence of this. Another problem with this arguement is that we don't know how much time passes between LBT 4 and 5, etc. As we may have heard, "Time heals all wounds." If a year or so passed, I can see that maybe they Gang had "moved on" regarding Ali.
If Littlefoot did feel as close as even the beginnings of "love" or even "sandbox love" as mentioned previously, I would have expected him to mention Something relating to her at some point. There have been 7 movies and 8 years (LBT 4 was 1996, LBT 11 was 2004) since Littlefoot has seen her. I suppose after this long (though we don't know how long this actually is, in LBT-time), there is a chance that Littlefoot has lost much of his connection with her.
What does seem slightly odd though, is that she is never mentioned in the more recent films to LBT 4 (LBT 5, 6). I would have figured that Littlefoot or somebody would have mentioned her at some point.
Another possibility though, is there hasn't exactly been a time in conversation where the characters would talk about Ali. They're generally distracted by something larger (lack of food, reunion with an old friend, enquiring into Doc's history, 'fixing' the bad luck) so that the relationship to Ali simply fell on the back burner in their minds. I can basically accept this as justification as to why Ali is never mentioned in later films.
Littlefoot and the Gang only knew Ali for a short while. Her herd arrived in the Great Valley in daylight. That same night, they set off for the Valley of Mists, they spent a full day getting there, and were home the next morning. They knew each other existed for a grand total of approximately 48 hours before Ali's herd departed from the Great Valley.
I can certainly see a friendship relationship beginning to grow after such time, but I doubt that the kind of love that endears the hearts of the Gang together could be as strong between Littlefoot and Ali, after such a short time together.
Then again, on the opposite end of the arguement, Littlefoot does seem relatively quick to bond with and make relationships with others. We saw this as early as his first meetings with Cera, Ducky, Petrie, Spike, Chomper, and later on, Doc, Mo, Shorty, and even Skitter. He seems quick to accept and enjoy spending time with new friends. Chances are, his relationship with Ali is no different. For Littlefoot, it seems, 48 hours is more than enough time to build a strong relationship. He is willing to accept others for who they are (eg. Chomper) and offers his help when he can (eg. helping Ali understand how different kinds of dinosaurs can be good friends, too).
Comparatively though, Littlefoot has known, grown with, and spent large amounts of time with the rest of the Gang for years (?). He has still only spent less than 48 hours with Ali, and even less than that, with just the two of them, one on one.
Even so, the love between Littlefoot and the Rest of the Gang is still probably on a higher, closer level than the love between Littlefoot and Ali. If Littlefoot were to run into another female longneck, I suspect a similar situation to Littlefoot and Ali's would occur. He would be interested in making friends relatively quickly, and would be excited to introduce her to the rest of the Gang. We seem to believe that this relationship between Littlefoot and Ali is particularily special. I'm sure it has a lot of value for both characters, but compared to what may happen if another female longneck comes along, it's hard to say. It's a difficult topic because we have never seen Littlefoot's behaviour with any other female longnecks his age. Just because she's the only one he's ever met, doesn't necessarily say that the two have a special relationship any different from the rest of their friends.