I think most places add it to milk. I supplement during the darkest six weeks of the year (which is starting very soon). It does seem like there could be a bigger seasonal push. Maybe not from the government but from somewhere.
I think this would be the best solution: to add it to the milk products during the winter! Most people would get it, there would be (almost) no public discussion about it and the immune systems would be strengthened. People not buying milk could still buy it like today!
This already is done year round. But there are a lot more vegans now.
Vitamin D is added in Alpro soy milk and the Oatly oat milk that I drink in Sweden, along with vitamin B12 and calcium. It's all equal to the levels found in cow's milk. There are organic variants of the above that don't allow fortification, but I choose the fortified ones.