I would like to see a snow biome, with players having to stave off the cold.
Polar bears, Penguins, Sea Lions, Fae Yeti's etc (whatever colours you like)
Snow storms as a new weather type that chills you to the bone, lowering stamina and sapping health. This could introduce new materials types that simulate thick furs.
There could be a mountainous landmass, or glacial flow, hopping from ice sheet to ice sheet.
A friend pointed something out to me the other day when I made a comment about it no longer getting cold at night in the forest. He said that, if anything, that's just another hint pointing at the next biome coming being a cold one.