We have 3D printers that can take a description and print an object. Some 3D printers are capable of printing everything needed to make another 3D printer.
This reminds me of programming language implementations.
An interpreter takes a description (a program) and prints some output. A meta-circular interpreter is an interpreter written in the same language that it inteprets.
With programming languages we also have compilers that translate a program into another program that does the same thing but better (smaller and faster).
What's the equivalent for 3D printers? I think it'd be a 3D printer that prints another, more specialized printer. That specialized printer might work faster or produce higher quality output or work with materials that a general-purpose 3D printer can't work with.
The analogy isn't perfect but I'd like to see 3D printers that print more specialized printers.