The developers have stated numerous times - Ice and Fire is gonna have ONLY Ice and Fire dragons, no other types. Many people before you have suggested other dragon types, but the mod is only going to have those two, which, in my opinion, is way better than having like 10 other dragons. First of all, that it's going to make the mod multiple times heavier, and it is heavy enough as it is, second of all, adding other dragon types will be completely against the mod's initial idea and lore. It'd be way better for the story if they instead focus on other aspects of the mod, like other mobs and such, which they're actually doing.
Thank you for informing me