So, for the last three seasons, I've ridden with shoe covers. That's three seasons featuring temps anywhere from -11 to 40F. My shoe covers are officially done for, but I'm having a hard time convincing my wife that I need pair #3 of cycling footwear. But I do have a pair of extremely comfy Salomon Equipe Combi CF boots. So I have a question/proposition. Has anyone ever tried to make a clipless pedal based on a cross country ski binding? I'm curious enough to give this a try. The pedal shape would be weird, but it might save a lot of people from having to shell out $300 for 45NRTH boots.

That'd be a whole lot-o pedal. Ski bindings are... huge. Say goodbye to having any sort of bag on the back of your non xtracycle bike.

I have dual sided pedals and just switch to the flats with insulated/waterproof boots. Most of the winter I can get by with my winter hikers which, with wool socks, are good down to about zero for a couple of hours. My heavy boots are much warmer and about 4" taller and with wool ski socks will get me 3-4 hours to -15 or so, or about an hour at -40.

I would think it would be easier to convert a ski boot to an SPD style cleat than a pedal to fit a ski binding, but either sounds like a bodge.

There are 3 or 4 types of x country ski bindings, but I'd think the attachment point would be the biggest issue. They all attach the boot to the ski in front of the toe. (at least the ones I've used)
Pedal clips are under the foot. I think this would not work as a result of this issue.