It's going to be hard to tax it when you can just print out another 3d printer practically. Sure they could tax the filament, but there will be ways around it. They will start selling spools of plastic and say it's for other purposes, or people will simply figure out easy ways of recycling their own plastics to make filament themselves. I highly doubt they will be able to tax 3D Printing enough to slow it down. The last 18 months we have seen the market practically explode with innovation, yet we are only at the tip of the iceberg. It's a fun industry to follow. I can't imagine what it will look like in 5-10 years, let alone 30-40.