You’ve either purposely, or accidently avoided answering the question.
You say there will be money to be made, but not on the end it’s made on now. That’s nonsense, as there are no ‘ends’ unless something is invented first. Without an ‘end’ no money will be made by anyone.
The basic laws of economics can’t be changed, something the argument is trying to do.
To answer one of your challenges; “Why invest in advancing metal production if everyone can buy a 100 pack of razors for $10 when each hand crafted razor is worth $100 now?”
Today, that inventor who creates a way to manufacture that 100 pack at a price which can be profitable is rewarded with a sum that reflects the ingenuity of his creation. If he can get the cost down a little below that $10 then he get a little compensation. However if he gets the price significantly below $10 he has the opportunity to be handsomely compensated.
Under the system you describe, we don’t know how he will be compensated, and that’s understandable. However, he must be compensated, otherwise he won’t create a way to manufacture those blades more economically.
I would envision a system not unlike what we have with media now. When a product is first designed and released it will likely be on a protected type of “one download one use” thing. Just like music and other info now, sooner or later it stops being new and hot and makes its way onto everyone’s hard disk. Or someone reverse engineers the dimensions and makes a free version.
I can also envision groups of designers producing entirely IP free things... like an open source engine. You print it out of metal... the design is free. You might actually start to see MORE interchangable car parts (just a wild example) as people settle on good free standard part designs.
I’m just throwing theory around here.
It will be easy to design and make the parts at some point. The money is going to be in the printers and the raw materials.