First of all, they can't leave everything unsaid! What's gonna happent to Astrid and Hiccup? I mean, I think they should make a third movie and have a kid in it. That would be totally awesome. If Hiccup and Astrid had a child, that would bring a whole new story. What kinda dragon would he/she have? What would she be like? I have questions if that ever happens.
Next, WHAT ABOUT HIS MOTHER?! What? Are you gonna just have us think of something ourselves? Nope. They need to make another movie to carry on the story! He was just reunited with his mom after 20 years for goodness sake! What will happen to her after this? Will she just be in the village and help out with crap?
Also, what about Toothless? He's the new "Alpha". That leads to him becoming the king, and who knows, maybe the king will find his pride (Night Furries). He would have new powers. And he could be able to do a lot more. I wanna know more about him now. That 2nd movie was epic. But Toothless has a longer journey in my head. And I want to see if they see it too.