When we were thinking about buying Nihola #1 two years ago in Denmark, we had really basic questions that we never got a good answer for before we tried for ourselves, such as the possibility of cycling up hills. Turn out hills are harmless, so now we've moved on to snowy, icy hills. Is that possible? (I can imagine that the risk of not being able to get up hills in the winter would be a huge barrier to someone who didn't already own two cargo bikes before arriving at the hills in question.)
I have Nihola-ed around in Oslo since last February so I know a bit of the answer already, but unlike then, I now need to get my kid up 70m of steep elevation climb in the morning, descend 175m (in a bit over 3km), pedal 7km farther to work, then repeat going the other way. Its actually a bit of a question if this is going to work all winter.
It snowed maybe 10-15cm (4-6in) on sunday and monday a week ago. The first thing I did was to go out there with the summer tires on, and no weight on board. (We were trying to go get a pizza.) Turns out a Nihola configured in this way can hardly move on flat fresh-snow-covered ground, but getting a 20kg kid to sit on the cargo rack enables respectable hill climbing. (Putting weight in the box has no potential to improve forward traction.)
So that brings me to the first lesson of driving a Nihola on ice and snow. Put weight on the back tire, lots of it. Everything that you are carrying should go back there, with the possible exception of kids. I would agree if someone were to declare its pretty stupid to have a big empty box in front, while everything is hanging off the rear rack with bungies, but at least the big empty box keeps the machine from falling over. (There is actually one kind of trike available in Copenhagen, Sorte Jernhest, which is front wheel drive with rear steering. So anyone who is really bothered by empty cargo boxes and full cargo racks can go buy one of those and find peace. Best of luck on the snowy, icy hills.)
The second thing to do is lower the pressure in the rear tire. How much depends on lots of things, but in a difficult situation it can go really low, just enough to keep the rim off the ground maybe 1cm when loaded. That is only advisable at low speeds.
The final magic is to fit a tire with helpful tractive properties. I am under the impression that aggressive tread (knobby) is a good idea on a Nihola because the three-wheel balance enables some digging, and studs are essential if anything is to be accomplished by the tire once it digs through the snow cover. For climbing on ice, the more studs the better, but studs really aren't going to do much on a hill unless you have first added some weight on the back tire, and set an appropriately low pressure.