Development of materials will always be at the forefront for 3D printing. The more materials available to print, the more applications that will be able to use 3D printing/Additive Manufacturing. Thus, materials will always have a high priority.
All additive vendors are working on or working with others to develop new materials for their processes.
One goal is to have the ability to control the levels of material hardness and softness over different areas of a build. Some additive vendors have been experimenting with this for a while now.
As for better ways to design with AM, that too, is a key need for AM to grow in use. Awareness is building. Industrial design and mechanical engineering are currently aware of AM and learning the best ways to design for its capabilities. A need now is to develop a multidisciplinary and interdisciplinary approach that could bring a broader understanding of the benefits of AM to other disciplines, such as manufacturing.
AM needs both the materials and the individuals that know what to do with them.