Ok, something interesting just occurred to me about our favorite Belly Dragger and Sharp Beak. It would make a lot of sense and could be an excellent plot line. It also might show, if I'm right, what kind of future Chomper might get if he ever did turn against Leaf Eaters.
Perhaps Dil and Ichy had lost their parents in some sort of tragedy or had been abandoned for some odd reason by their parents. They were found by Leaf Eaters, who, like the Gang of Five, had realized that perhaps they could be nice.
They may have lived with Leaf Eaters for quite a while, which would explain why they can talk Leaf Eater. They might not even know the Sharptooth language, which also explains why they are practically the only Sharpteeth that have been on screen for a long period of time not to ever use it.
At some point, perhaps nature took over for them and they attacked/killed a Leaf Eater. They then had to run for it. Dil might have been injured in the chase,hence her eyesight problem.
Dil and Ichy may have lived there and met before both having to flee. Perhaps they met near the place where they'd long lived (maybe they lived with separate groups of Leaf Eaters but still nearby) and they helped each other escape, hence their partnership.
Anyway, as they never lived with Sharpteeth, they didn't integrate with their own kinds as they couldn't and sort of ended up living as outcasts and together near the Land of Mists.
Were Chomper to go bad, other Sharpteeth still might not accept him for all the years he was odd and also his Leaf Eater friends wouldn't like him anymore so he too may end up living alone in a place like the Land of Mists.
Also, the sadness of what happened with the Leaf Eaters in their past and other things may explain why Dil and Ichy have trouble getting along yet they don't really leave each other (Dil looks like she was looking for Ichy at the end of IV.)