I have found at least in my area the best option for my needs is to eliminate the rear derailer assembly but keep the rear spool of cogs and just loose the ability to remotely shift gears on the rear and instead us some old rear derailer parts to build a chain tensioner mounted to the chain stay that keeps the chain tight and tucked up high and tight. I keep the front derailer on a triple front crank which gives me a three speed with gears that actually shift in the cold and don't ice up badly under most conditions. Changing gears on the rear spool means stopping the bike and getting off and manually moving the chain by hand to a different cog on the rear.

In my experience for winter riding IGH just rust themselves to pieces with water and road salt getting inside and freezing and thawing and freezing and thawing and they can't always take the punishment I can dish out to them. Rear derailers ice up and jamb up (mainly due to hanging down low in the snot while being expected to both accurately indexing the chain on the rear cogs and keep it tight, mount it up high and flat and set it up so it only has to keep the chain tight and you eliminate a lot of the trouble) so that is the main weak point, also the rear cogs ice up way worse then the front chain rings so much better chance of being able to successfully shift up front then in the rear. In addition the front derailer is pretty easy to "armor" against the snot getting into its mechanism and freezing and locking it up compared to the rear especially if you use a front derailer that has the cable come down from the top into it rather then the kind with the cable coming up into it and forming a low loop to collect moisture and ice up in that spot. Long story short, you can fix up a front derailer set-up so it is pretty reliable to give you three gears shiftable on the bars on the fly in winter weather, rear derailer is a lost cause so just elimate it and build a chain tensioner tucked up high and tight mounted on the chain stay.

If you have to stop and get off the bike to move the chain around on the rear cogs you can wire brush the ice on them if needed if all but the one you have been using has iced up and it isn't like a huge extra hassle to do so since you already have to stop and dismount to move the chain on the rear cogs anyway. Also your not tempted to try to make it shift when you shouldn't and try to grid the ice off the cog you want to shift too by letting it grind and slip hoping it will catch soon, removing temptation and all that jazz. Normally I use mainly the rear spool gears on a bike and just use the front chain-rings for big range changes like when going through a hilly area or such. Winter set-up just reverses that with three main gears I use to shift the vast majority of the time on the front derailer and front chainrings which are reasonably reliable for good shifts even in the winter under adverse conditions and use the rear cogs to make big gear changes by stopping and moving the chain to a different cog on the rear. You will want to carry a toothbrush like wire brush in your coat pocket to brush the rear cogs if necessary.

Works for me.

I have been winter riding now for five years.

I do the heavy oil thing at the start of the winter, I also use Grunge Guards front and rear. I have never had any shifting issues.

In the spring, I replace the entire driveline--crankset, chain, and cassette.