I can't tell if you are being sarcastic, but I'll bite. My guess is never. CNC plastic printing has been around for 30+ years, and is only practical for making one of a kind parts. As soon as you are making something that 1000 people need, there is a better manufacturing method.

Maybe I lack imagination, but I cannot imagine a plastic piece of junk that need to be tailor-made poorly.

When the cost of a PC went from $30k to $2k, most people couldn't see the revolution happening. Maybe I am the same fool.