I think noonespecial's point is that much of Ikea's income comes from people meandering through these labyrinths, being exposed to item after item until they see something that they "must have". It would not make sense for them to cannibalise this by completely changing the business.

You do raise some interesting ideas, and I think there is a place for 3D printing in Ikea's business model, especially in customisation of off-the-shelf items.