My only gripe with single speed in snow is when the snow is quite deep I want lower gearing than when the roads are clear or close to it. Since the roads are clear the vast majority of the time in winter around here, I want my gearing close to what I use the rest of the year. But I really appreciate those lower gears on my mtb when trudging through miles of snow several inches deep. My derailleurs do get frozen up with ice sometimes. I have been thinking about a winter build with an IGH, but I understand those can get sticky in really cold conditions too.