Here's my short answer. lol
Same 5 bosses for now.
New Abomination creature in the Swamps(New Armour from roots).
Tar Pits in the Plains for upgraded building pieces and Lox taming(Make a saddle for Lox to ride).
New Caves in the Mountains with new creatures which leads to new weapons and more materials for building.
Mistlands update upcoming in the future.