Has anyone addressed whether new winter activities will be usable outside of Mt. Komorebi?

Good question. I honestly doubt it. Everything seems to be pretty restricted to one world. The animations for Skiing, sledding and snowboarding appear to only work on very specific locations in that world. It’s not just snow, but probably the routing of the terrain has to be made to work with those animations. It’s probably similar to swimming in other worlds. And I doubt the flat snow in other worlds will be formatted for any of the activities in this pack.
I’d be happy to be proven wrong though!