Some interesting ones can be found here: http://www.berksgrapevine.com/2012/11/sketches-of-adult-hiccup-and-astrid.html
Apparently, it will be much more multicultural - which makes sense, because what kind of Vikings DON'T explore other places and go and raid and pillage and whatnot? And they have freaking dragons - like, their mounts were born for good ol' Viking raids.
But, you know - if they've never been outside of their island before...how will they know where to go?
But the most important tidbit of all? All the characters will be 5 years older, and Astrid and Hiccup are going to be HOT.