It was a preview release, but they've already started rolling it out to the regular Nightly channel and according to this very blog post we're discussing it's supposed to have a "public release later this spring".

Given that any changes have to work their way through the Beta channel, too, there's not much time left for landing changes in Nightly that will still make it into the first Release version... so the first official Release version that will be pushed out to everybody will indeed be in an unfinished state.