I was about to ask about the motivation behind these changes in the implementation language, but the FAQ explains it all (last question): http://pijul.org/faq.html

Why is Scala considered "not open enough" BTW? Just curious.

Oracle's control of JVM and less community democracy compared to LLVM and rustc (what is used in Rust) may be what the mean, I suppose.

That paragraph sounds pretty uninformed. I wouldn't take it too seriously.