The problem is that updating a terrain can be a big job (bigger than we think, as Dux is on it, a master terrain guy, and he says it's being a pain). So that alone has to be done, and that's just for dealing with rhinesum. Once rhinesum is done, it is used as the basis to make rhinewin, so winter tiles then need to be made. Once you add in that people also would have to design winter skins for every ground vehicle, skins that have to be approved then put into the terrain, all of that work together takes it well outside the realm of what can be done in the time available.