For me, the the most difficult thing about winter riding has been keeping my feet warm on cold extended rides. Of course I have found several solutions that work to keep my feet warm in varying degrees. But all the solutions that I have found so far have been wanting in some critical area of performance. The things that really kept my feet warm for long periods of time were heavy and so made the riding less enjoyable and reduced the distances I could ride. Seriously, it is not fun to be wearing 2-3 pound hiking boots on each foot when you are used to 12 ounce cycling shoes. Try riding at 80-90 rpm cadence for long periods with heavy boots on and the riding gets tiring quickly. The heavy hiking boots also bind at the ankle to some degree and of course if you want to use clipless pedals you are faced with the dilemma of drilling holes in the bottom of the soles and doing some custom sole work which can render the boots less usable for other things.
My present strategy is to use either a dedicated pair of winter cycling boots (Answer Kashmirs) with thick wool/acrylic socks or to use a layered method of neoprene sock/wool sock/oversized shoe/shoe cover. The Kashmirs are very comfortable but limited in how cold and how long I can ride with them. The layering method seems to have about the same coldness and time limits for me. I can ride for about 45 minutes down to 20-25 F then my feet will get cold.
There are several reasons why I believe that this is the case and I will detail some of the technical reasons why I think the typical winter cycling shoe strategies are not that good.
Anyway last year I came up with an idea that would be reasonably inexpensive to implement. But it would not be dirt cheap. I was however, too busy last year to work on the project but I think that I want to try to do it this year. And my plan is to document what I am doing here with pictures and explanations so that if someone else wants to try this method out they can try out my idea.