I don't follow this project very clsely, so there probably already is an answer, but I' gonna ask anyway:
Why 12 witnesses exactly? How is this nuber determined? What would happen, or what would you suspect to happen, if you had, say, 120 witnesses?
saw this is discussed in white paper. The number should not be too small to prevent fraud, yet can't be too big as it will be managed by each user.