Actually the printer side of things is about 90% there.
You CAN buy an off the shelf printer that does not rewuire any assembling, and you can get them pretty cheap and they are near enough plug and play.

That's NOT what's holding up having a 3d printer in every home.

The simple truth is that no matter how easy to use a printer gets - you STILL need to be able to use cad software and design the things you want to print.

It's the 3d scanning side of things, that is really holding things back.

There have been a couple of attempts to make 3d photocopiers,

xyz made one - that by all accounts was atrocious and a company called AIO made the ZEUS scanner/printer/copier. Which - while not perfect could actually do 3d photocopying.
https://www.youtube.com/watch?v=Ik3SwIDlYPA

I've heard nothing in recent years and the whole 3d photocopy system seems to have died a temporary death.

Also for every home to want a printer, the big hardware manufacturers need to wise up and start using virtual part stores.
I mean you can store all your speare parts on a server and do away with warehouses and manufacturing chains. You'd actually end up with a server and customers not only paying you to download the file, but also paying for their own plastic to manufacturer the parts.

On a side note, while this guy is talking complete and total bollocks about fdm print speeds, this lightweight extruder looks really interesting:
https://www.youtube.com/watch?v=7IJaD15UQU0

But to sum up, in order to get a microwave style 3d printer, you need idiot proof 3d scanning and a whole new manufacturing infrastrusture and change of approach to spare parts.

The printer technology is there, it just needs everything else to catch up with it.