Indeed. Who would have more than one material to print with? Well, probably everyone. And material science being what it is, you can imagine it won't be long before we can combine materials in ways previously unforeseen.
There's also an implicit assumption here that the design of objects will not change to support their production method. So, if we're limited by size or number of materials then designers will adapt to those constraints.
> Who would have more than one material to print with? Well, probably everyone.
Currently the number of materials you'd need to stock in your home to be able to print various kinds of products would be quite large (20 or more). That doesn't make sense from an economic perspective.
Let's image, then, that we'll see products made from fewer raw materials because the design changes to accomodate printers. What reason would designers/manufacturers have to do that when they know they won't be able to make a living when their products get pirated?
I agree that it doesn't make economic sense now to hold various types of material, but then I guess laser printers and cartridges used to be pretty expensive too. I'm thinking long-term here.
> What reason would designers/manufacturers have to do that when they know they won't be able to make a living when their products get pirated?
The same reasons people still write software and make music, even though they know their products get pirated - you can still make money from it. I agree though, it will be a completely disruptive innovation from the point of view of designers and manufacturers.
There's also an implicit assumption here that the design of objects will not change to support their production method. So, if we're limited by size or number of materials then designers will adapt to those constraints.