I would have to guess that the biggest reason people avoid fishing in the winter is temperature. But people still ski, snowmobile and recreate in other ways in the winter? If you can stay warm while riding a lift or buzzing across the snow covered hills on a snowmobile you can stay warm while fishing.
Here are some ideas to keep you happy on the river this winter from the ground up:
Don't let cold feet get in the way. Cold feet are the biggest culprit when it comes to calling it an early day. Wear thick socks like Simms ExStream Wading sock. They're super thick and insulating and draw moisture away from your skin. Also, try a thin liner sock or antiperspirant spray to draw moisture away from your feet. Some people will put tow warmers in, but they're often bulky and hard to place just right.
Start warm, stay warm. Overdress for the occasion. You can always shed a layer if you're too warm, but once you get chilled it's going to take a lot of time to get your core temp back up.
Layers are your friend. As with your feet it's a good idea to have next to skin layers that draw moisture away from your body. A side not, most of you now use breathable waders, which are only as breathable as the layers you wear underneath. on top of your next of skin layer thick long underwear work great and the more skin they cover the better off you are. For your outer layer try to stick to breathable materials too, but maybe something that also sheds water like a raincoat. Ski pants can also work well, but tend to be bulky.
Accessorize. Hats, gloves, Buffs, scarves and more. There are a ton of accessories available designed to help keep you warm. Simms ExStream series gloves are some of the best at keeping your hands warm while offering options to maintain dexterity. Buffs aren't just for keeping the sun off your face and neck in the summer. They make a wide variety of fleece and wool products to keep you warm while you play. Hats tend to be extremely personal and way to express your style, but it's important to have a hat that covers well, is wind resistant and a bonus if it sheds water too.
Prepare. Applying Loon Ice Off Paste to the guides of your rods in the comfort of your warm house the night before is highly recommended. This will greatly decrease ice build up on your guides. Applying while the rod is cold is not as effective. While you're at it rig up your rod, so you're not doing it on the side of the river with fingers that could still be warm! Line your clothes, waders and boots up in front of the heater before you put it on.