Last summer I built up what was going to be a dedicated winter bike. I started out with single speed coaster brake. I needed a very low gear to get moving if I got bogged down in deep snow, ruts, slush, etc. Halfway into the season, I strung up an old Sturmey Archer 3 speed coaster hub that was in my bin. It was a massive improvement. One nice thing about IGH is that they are much more tolerant of the condition of the chain. I put a pre-rusted chain on that bike, oiled the hell out of it, and it wasn't any more rusted by the end of the season.
I do like the idea of an enclosed chain case. I'll keep my eye out for one that fits on my bike. For now I have just a chain guard, which is at least a step in the right direction. It actually helps a lot because a lot of the salt slush hits the chain from above as the wheel comes around and sprays **** everywhere.