I say 5-10%. 3D printing is catching on, but I don't think it will catch on that fast.

If Staples really puts one printer in every store - and perhaps some other companies with FFF plastic printers - then it's a more likely scenario I think :-)
That's such a brilliant idea. Even other stores like Home Depot, or grocery stores might benefit from having 3D printers in store. It would certainly bring customers in.