I wish the author has written about the motives behind the language and why someone should choose Copper. We have in fact more programming languages than we actually can use.
It is a personal project, which the author uses for some other personal projects.
Clade - a programming editor with elastic tabstobs and Smalltalk like navigation
Maybe, there is more. Looks to me like an illustration of the "It is a quiet life" meme
Author here. I have written this language for many reasons but I won't detail here, I'll just say it's a lot of fun for me to design a language and write a compiler.
This language is a playground where I constantly add and remove features or try various experiments, so I have no intention to promote it. The only reason I have published it is that I publish an open source text editor written with this language.
After twenty years of evolution, it starts to become stable but not yet, I had recently added some basic option types.