That could be a nice plug-in. [:)]
The difficulty depends on your programming skills, but you could reuse many classes of Sweet Home 3D to help you achieve it faster. To avoid having too much to master, I would:
- learn how to program a new plug-in,
- program a dialog box that would let the user choose the image on each side of the cube,
- generate a cube at OBJ + MTL formats (generate one with Sweet Home 3D or better with an other 3D program and you'll understand quickly what it requires),
- gather the OBJ, MTL and textures files in a zip file,
- create a modifiable CatalogPieceOfFurniture instance, and add it to the catalog (and/or add it to home after that if you want it to appear in the plan), reproducing the behavior of the finish method in ImportedFurnitureWizardController class.