How close is Bun's Rust rewrite to production readiness?

Bun's development team recently achieved 99.8% test compatibility on Linux x64 with glibc in their experimental Rust rewrite. This is a significant milestone for the JavaScript runtime, but it raises some interesting questions about what this really means for developers.

For those unfamiliar, Bun has been working on rewriting core components in Rust to improve performance and reliability. Hitting such a high compatibility percentage suggests the new implementation is handling nearly all the edge cases and behaviors of the existing codebase. But that 0.2% gap is curious—what's actually failing? Are these known limitations, or are there deeper compatibility issues lurking?

The focus on Linux x64 with glibc is practical but worth discussing. When can we expect similar progress on other platforms like Windows and macOS, or architectures beyond x64? Production environments are diverse, and developers will need confidence across multiple deployment targets before widely adopting a rewritten runtime.

What does this compatibility metric really tell us about real-world usability? Test compatibility is one thing, but how does this translate to actual npm package compatibility, edge case handling, and performance gains in actual applications? Are there specific use cases or packages that might be affected by the rewrite?

If you're following Bun's development or considering it for your projects, what concerns do you have about a major rewrite like this? What would make you confident enough to switch?