Yes, because SGDK2 is based on Direct3D (or OpenGL, if you're planning on using 2.1) you can theoretically do "boxular 3D" if that's a real term. But you would have to write most of the code to do this yourself. You would have to understand how to code for Managed DirectX or OpenTK (the OpenGL library used by SGDK 2.1). SGDK2 makes 2D games relatively easy by providing a framework, but it does very little to help you with a "boxular 3D" framework, so that will be relatively much more difficult (partly because there's no framework and partly because it's naturally more complicated). So yes, you'd kind of have to be a wiz kid.