Also excited about the Rust compiler! Apologies if this is far from reality, but by looking at recent commits in GH[1] it looks as though this has been rushed for a v12 release, so I was wondering how much of internal testing has this been going through before pushing it to the broader public.
We've been testing SWC for months now, both with early community members on canary releases and with Vercel customers. Lots of the rushing at the end was for minification, which is opt-in because of this. But compilation with Rust (replacing Babel) is stable (which is why it's on by default).
[1] https://github.com/vercel/next.js/commits/canary