Ah, but I'm not proposing that cyclists wear several layers of thick socks. I never go with more than one thin sock as a base layer and a thick wool sock on top. That way, I don't have to wear shoes which are more than one size bigger than I normally wear.
And, in my case, I've got very narrow feet, so I've got extra room in most shoes anyway. I know that will not necessarily be the case with everyone.
I too believe that an outer covering, over the shoe, is a better choice than going with too many multiple inner layers. The double layers of socks in a slightly looser shoe will work for temps above the freezing point (and apparently it works for some below the freezing point too ... but not me), but as I approach the freezing point, I need to add some sort of wind-resistant bootie. That's where the nylon bootie comes in. They are good because they do have some breathability ... or maybe I should say "venting". If it is going to warm up, or if it is chilly but not too cold (situations where your feet might sweat), then that bootie is the right choice.
The neoprene bootie works well for me in colder temps.
To create additional warmth, without overcrowding the shoe, a person can use chemical warmers, as I mentioned on the webpage in my first post. The chemical warmer can be placed outside the shoe, on top of the toes, but under the bootie, so the bootie holds it in place Because most cycling shoes have mesh over the toes, placing the chemical warmer there is quite effective to keep the toes warm.
But I'm curious ... what sort of shoe cover are you referring to? Is it one that exists? If so, could you post a link to it? If not, is there a way you could draw it? I'm not sure I'm picturing exactly what you mean. When I first started cycling in the winter and was suffering so badly from cold feet, someone suggested that I wear a wool work sock OVER my shoes ... and another person suggested duct tape over the venting on my shoes. Would your suggestion be a combination of the two? Something like a wool work sock over the shoe (the high loft part?), with duct tape overtop (the windproof part?)??