Another solution could be to program a half replacement, i.e. keeping a 3D API very similar to Java 3D API, but changing its implementation with more direct calls to OpenGL through JOGL and keeping only parts needed by Sweet Home 3D.

The 3D API of jMonkeyEngine being close to Java 3D, what do you mean by half-replacement while keeping the parts necessary for Sweet Home 3D?
Although some methods in this API have the same name or have the same functionality as Java 3d, their sub-methods are different.

Replacing Java 3D by an other library is similar to the quest of finding a better rendering engine than SunFlow. It would require a lot of time, and even once you reached a working solution, you might have some bugs difficult to fix.

Since Java 3D uses the GPU and manages the lights (ambient, directional, point and spot), how to adapt the [font=courier new]PhotoRenderer[/font] class to use Java 3D as a less photorealistic rendering engine?