I would really like to see schools of small fish swimming upstream and maybe bears hunting them
Doubt it will happen though.
iirc in skyrim there is a clan of vampires that live in frozen lakes. Could be fun - there you are just walking casually on ice, and suddenly you are dragged under water, you are running out of air, trying to fight blindly under water while trying to find an opening in the ice so you could escape. Could be epic
EDIT: As for air creatures... well, maybe we can have daedra seducers from daggerfall back. Naked chicks with wings :hubbahubba: