The biggest secret in being able to run barefoot comfortably in cold weather is achieved while sleeping!
Try this out: Remake your bed so that the sheet is turned back not just at the head but also at the foot. Then add a down comforter or a couple more blankets to what you usually use. When you go to sleep, let your feet stick out into the cold night air. (No socks allowed!) You want to be HOT initially. In a short while the blood vessels in your feet will dilate, allowing excess body heat to be dissipated via your feet. This feels a little odd at first, so it may take a bit longer than usual to fall asleep. Allow some extra rack-time initially to allow for this.
Such “vascular training” will let you run in the cold with complete comfort. Example: Yesterday I ran and hiked for three hours through Clifty Falls State Park in southern Indiana. The ground was snow covered, air temp. 24 deg., and the trail crossed and recrossed a creek such that my feet were repeatedly immersed in freezing water. It was very windy with snow flurries. I was wearing Soft Star RunAmoc minimalist trail-running shoes (w/o socks).
No exaggeration in saying that my feet were not just pain-free but TOTALLY COMFORTABLE at all times. I’m not some kind of masochist or freak-of-nature; you can do this too.