This bonsai was grown from seed and kept in a small container for its whole life. Development of a bonsai for size will occur most quickly in the ground or in a large container. Although growing in a large container or ground growing can develop large bonsai often the tree will need finer branching and detailing. This should happen once the bonsai is containerized and nearing its final size.
Now that the size and branching are nearing a reasonable point, leaf reduction and increasing branch density will be next on the list for development.