I'm now transitioning from surf, to skate and MTB, as off-snow emphases for the near term, though I'll still do some weekly pool time because muscles are very vindictive if you don't call and talk from time to time.
In terms of specificity, mtb and shortboard surfing are pretty good complements to on-snow ski and ride imo, and skating is in some ways, and is not in others. Balance for skating is different enough that while it is good crosstraining, it imo is in a different couple categories (shortboard skating, longboard, and pump-focused skating I'd really put in three categories, in fact).
I will also be getting in a couple trampoline sessions over the next couple weeks, and it will be interesting to see how much I've lost. The crossover in terms of air awareness from the summer tramp work along with some cliff jumping and diving has actually been good, if at a low level.
To add to the clutter, I am breaking in a new dog. What that really means is that a portion of my aerobic base is done with the dog one way or the other, wether jogging, on the bike, steep hikes, or the dog towing me on a skateboard. I'd be doing most of this anyway, but probably have been a bit more aerobic even than my norm because of the dog variable.
The clutter is not optimal in terms of fitness, but keeps it fun for my short attention span.