What is the state of const generic (RFC 2000)?

On May 2017, this RFC was discussed, and it was predicted that this feature can be available in the nightly version. So what is its state now? If it was introduced into RUST, it could bring significant convenience especially for lib design.

(Not sure whether it is proper to raise this question in internal.)

There is a tracking issue for the feature, here it is Tracking issue for const generics (RFC 2000) Follow the issue the feature has not been implemented yet, but maybe will be implemented later this year.