[rntz]

Author here. I have created a language, called moxy (https://www.github.com/rntz/moxy), which supports not just extensible pattern-matching but defining extensible extensions in general (of which pattern matching is one example, LINQ might be another, and so on and so forth). However, it wasn't a lisp, because I also wanted to see whether I could support syntactic extensibility in a non-lisp language.

The really important point, that moxy explored and that I think I didn't make clear in the article, is that patterns are just one example of where you want extensibility of a non-expression syntax class. Really you want to be able to define your own syntax classes and be able to extend them!

I only mentioned moxy in a footnote in the article because it's "research-quality" at the moment - it's not well documented and I'm still having second thoughts about its design. I've moved on to other thing and am busy with work, so I don't imagine I'll be working on it in the immediate future.