December weather can be very mild, although a little gloomy, and a great time to hike. Just be flexible. Do you know your cold tolerance level? My tolerance level is fairly low but have hiked many times in December.
I'll be finishing up the BMT early next summer, just have the Smokies left. If you decide to hike in June and want a partner for part of the way, let me know. I only hike with other ladies though.