If you look at a map of Tamriel, you'll notice that Skyrim is surrounded by a fair few countries: High Rock, Hammerfell, Cyrodiil and Morrowind. Hammerfell and Morrowind are traditionally considered to have vastly different landscape from Skyrim. As much as some people want to avoid real world locations in this thread, take a look at a map of Russia. It's surrounded not only by cold looking regions such as the Baltic states and Scandinavia, you also countries with very Asian feels such as Azerbaijan, all of Central Asia, Mongolia and, very notably, China. No need for just icy Himalayan looking mountains and bare tundras, you can also have dry grassy steppes and coniferous forests thrown into the mix.
Geography aside, the culture alone could be extremely varied due to border influences. Russia's not ethnically homogenous Slavs, there is a significant Turkic minority, some of them totally indigenous (I'm thinking Tatars in particular). Why not have indigenous tribes of Dunmeri or Yoku decent, as well as immigrants? A lot of the ethnic tension and nationalism could lead to some unique factions and quests, as well as some great atmosphere such as unique dress and cuisine. That's not even going into delving into the typically fantasy additions of bestiary, magic and whatnot. The sky's the limit for Bethseda if they look at it the right way, should they choose Skyrim as it's next location.