What's the limitation on adding additional vertical layers though? One apparent limitation could be that by adding several vertical layers it would require the wire to be longer.
1. Heat doesn't go away with layers and gets harder to cool.
2. These are still layers. You want each layer to be as flat as possible. As the layers deform you lose the ability to cleanly add more layers.
Current lithography is very much based on the notion that everything is flat.
