I solve that one by not using boots. One of my hiking partners liked his goretex boots for the snowy section (he switched to trail runners in Virginia), but I was happy with trail runners throughout. Feet get wet, not a problem with wool socks, though I did use goretex socks (over the wool ones) at times.
Shoes are at least a little more flexible when actually frozen (this only happened a couple of times). I just put them on at the last minute, just before starting to walk, so as my core body temperature rose (through exertion) my feet could eventually warm up and defrost the shoes --- uncomfortable for the first half hour or so and then you forget about it.
Give me frozen shoes over frozen boots any day, yet another benefit IMO of light footwear. And if boots and shoes do get totally wet, the shoes can get completely dry from just a NERO.
Caveat: again, don't try this (shoes not boots) for the very first time in snowy conditions at the start of a thru-hike ...
On a related note, one of my favorite pieces of gear for the early stretch was a pair of
Feathered Friends down booties. They definitely add weight and bulk to the overall gear load, but were very very nice to have at the end of the day and to keep me warmer in the bag at night, and the shells made them decent footwear for "close by" the shelter. Worth carrying (up until Damascus, maybe Pearisburg).