I'm usually not one for speculation, but the Sims team has hinted towards a winter retreat type pack 3 different times now this year. That's gotta mean something. Hint one: In the community survey ...
Knowing the Sims team, I would say: yes, I think the snowy mountains in the back of Evergreen Harbor are a hint to a new Winter Retreat pack. I remember in SIms 3 Ambitions you could zoom in the horizon and you could see a bustling city full of skyscrapers, and later they released Late Night with apartments and Bridgeport.
Anyway, I remember that theme being in another survey before 2017. idk why its taking so long for them to make this winter themed pack.