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I ski with a backpack all the time-- sometimes with a camera, sometimes just my avalanche shovel and probe (the beacon has it's own sling against the body, under the jacket).
Important considerations are chest and waist straps that you can get relatively snug. That prevents bouncing when you hit any jumps. Others include straps to tighten down the bag so that loose stuff inside doesn't bounce around too much internally-- both to protect those items and because it makes the skiing more fun. OR, having enough stuff/padding in there to keep everything in place and calm.
Honestly, provided you're not taking yardsales against icy moguls, protection FOR the camera isn't a big deal. Although with a 70-200 mounted the leverage if you hit just right could damage the mount interface. I'd be concerned with whatever's in the bag not being padded enough that it becomes a hard fulcrum under the spine AKA protection FROM the camera. But... I may be biased in that earlier this summer I took a massive pile-driver on MTB that resulted in 3 x thoracic vertebra compression fractures (a relatively minor injury... I did a 100+ mile ride 3 weeks later).
Bottom line: a secured pack, and stuff it with a fleece/extra t-shirt. The camera is going to be fine. Personally, I'd rather keep one or two light/short primes + camera (one mounted) if I'm skiing to ski (perhaps 35mm and 85mm) rather than a big, long mounted zoom. The zoom is more useful for instruction videos of a skier, in case you want to follow their movements as they approach and pass you for teaching purposes.
Another consideration: Wear mittens as the outer, and fingerless, lightweight gloves (or just really light/tight gloves) as liners. And see if your mittens have a strap that attaches to your wrist or jacket. Makes it a hell of a lot easier to drop the mittens and work the camera without having to do multiple pack/hold/unpack/hold movements.