The guy who has the limb owns a portable band saw, the only straight pieces are just a few feet long, most of it is curvy & twisted.
The curves were what original got my attention, my first thought was to use one of the arches to make a nice rustic head board for the bed, peel the bark & clean it up, add some large knotty spindles to fill it in, but when I found out it was black walnut I got other ideas also.