Seriously, I want to see the former homeland of the Khajiit people, possibly be able to play as various other subspecies of Khajiit (There are apparently larger more hardy mountain Khajiit, and more slender and smaller forest Khajiit, etc.).
One of the books in Oblivion referred to the Khajiit fighting for the independence of their homeland Elsweyr, and that if they can't have their homeland, they have no qualms about making the entire nation uninhabitable. They put no real value on architecture which can be rebuilt, as their true histories are passed orally from parents to children, and not kept in books as the availability and fragility of paper and pen devalues the words and history of the family and people.
Also, I expect that there are subsets of Argonian and other races, maybe regional varieties of Orc and such that differ from the general ones used in Morrowind and Oblivion and such.