You can expand this as much as you want, as long as you take off the plastic cover it comes with to protect before purchase. Just lift up the front inside flap, remove screws, add more posts, add your pages, then screw cover back on. The cover and the center binding are separate.
Keep in mind though, that the matching center binding will only expand a certain amount, so if you want to keep it looking like a book with a spine, then it is limited. But I have several scrapbooks that have no spine. Just a top cover, inside pages, and a back cover and they look just fine to me.
The middle spine is just paper of a matching color. You could make a larger one no doubt.