The plan was always to get on stable[1]. Sergio just wasn't willing to compromise on the API to make it happen sooner and I appreciate that since it's a motivation to stabilize the things Rocket depends on. The release notes being discussed here mention that Rocket should be on stable with the next major (Rocket) release.
To be clear, it means the next major release of Rocket, not Rust (I misinterpreted your comment and had to go look, so I thought I'd save others time if they also misinterpreted your comment.)
[1] https://github.com/SergioBenitez/Rocket/issues/19
edit: specify Rocket release, not Rust release