Why does a winter-terrain need to be a separate terrain? Wouldn't it be sufficient if for every terrset X there's a corresponding terrset Xw, which is... white? All trees at the same spots, except covered in snow instead of leaves?
Again, the default skins are NOT winter skins and that makes them stand out in front of any white winter background. So to clarify, anyone disabling skins will not see your attempt to use a winter skin on the current winter terrset, they'll see the default green summer skin currently. So trying to use a winter version of any current MA terrain would have issues unless the winter version came with default winter skins for the vehicles.
The nice thing about this is that you could still use a non-default winter skin on
your vehicle and even if someone has skins turned off, they would still see the winter default while you see your non-default winter skin. That means it would work exactly the same as the summer set of skins now. I've seen guys driving around in the winter default jagdpanzer 39 skin on a summer terrain making them an easy target. Same kind of thing in revers, checking your skin before you leave the hanger would matter.