I'm surprised to see no one comment on Zig. It seems like the bun.sh developers are making some bold changes with such a low-level language.
To give another example of where this came up: they were discussing using Zig for the Ruby JIT, but despite really liking Zig the team decided to go with Rust because of its maturity: https://bugs.ruby-lang.org/issues/18481#note-21