Earlier quoted context omitted.
A little over 18 months ago, 1.0 was released. We've had very strong compatibility guarantees since then.
While that is true, in Go, almost no libraries are written to use non-stable features. This is not the case in Rust.
To recap, in Rust, to make additions to the language:
1. Small additions mean make a PR.
2. Big additions mean make an RFC, then a PR if accepted.
3. These PRs go behind a feature flag that lets us track the feature, and only allows it on nightly.
4. People who desire the new feature try it out. (This is what you refer to.)
5. If any issues are found, they're fixed, or, in the worst case, the feature is removed.
6. The feature is made available to stable users, the feature flag is removed, and backwards incompatible changes can no longer happen.
What would be un-healthy is if everyone had to rely on nightly for everything. At the moment, most people use stable Rust. And of the people that use nightly, the largest single feature will be stable as of the next stable release for Rust. But some people are always going to be using nightly features, and that's a good thing: it means that by the time it hits stable, it's already undergone some degree of vetting.