So, people printing stuff out of PLA plastic on an extrusion printer as a hobby means what, that product design as an art is going away? Will an army of hobbyists with the much improved descendants of Makerbots make employing someone like Jony Ive obsolete in 50 years?

It sure looks like that - it appears to me that Marx's "workers owning the means of production" argument for collective ownership of workplaces is being conquered by tool prices going down by successive orders of magnitude.