This title implies some things that aren't quite right. Let's take a step back.
The current release of stable Rust is 1.13, beta is 1.14, nightly is 1.15.
New features land on master, hence 1.15. So this means that, if it does land, it will become available on nightly soon. But it's still behind a feature flag. So it won't actually come out in Rust 1.15.
I am not on the relevant subteam here, so I am not 100% sure of the procedure, but usually, stuff has to sit in nightly for a full release cycle to be eligible for stabilization. So if this lands tonight, it'll be in nightly 1.15, 1.16 will be its full cycle, and it'll be elligible for release in 1.17, which would be March 16, 2017.
The current release of stable Rust is 1.13, beta is 1.14, nightly is 1.15.
New features land on master, hence 1.15. So this means that, if it does land, it will become available on nightly soon. But it's still behind a feature flag. So it won't actually come out in Rust 1.15.
I am not on the relevant subteam here, so I am not 100% sure of the procedure, but usually, stuff has to sit in nightly for a full release cycle to be eligible for stabilization. So if this lands tonight, it'll be in nightly 1.15, 1.16 will be its full cycle, and it'll be elligible for release in 1.17, which would be March 16, 2017.