Now that we have end-user programming environments capable of empowering kids with no programming background to build games in a matter of hours, a new quest for raising the ceiling of enduser development is emerging. Environments not only focusing on programming, but also including rich media such as 3D, could work as compelling tools for introducing information technology at the K-12 level, addressing even the problem of dwindling numbers of computer science student enrollments at universities. The new challenge is raising the ceiling without raising the threshold. Based on our experience with AgentSheets, which has been used worldwide for computational science and game design applications, we created a new authoring tool called AgentCubes. This article discusses the notion of Incremental 3D as a design approach for media-rich end-user development with low threshold and high ceiling in education.