I've never really thought about it, but if I have the skills or technology, I'd like to make something with a ton of customization and upgrades, not necessarily voxel based, either. I mean something along the lines of, making a tool, combining components made of various materials or metals, like a sword with a blade of (metal here) and a handle of (material here), or armour with types or materials of padding, like leather armour padded with cloth, etc.