Paul Turley points out a blog post from the Reporting Services team:
When will we have this next Technical Preview?
We’re targeting January 2017 to release this next Technical Preview.
What’s the release vehicle for a production-ready version?
We plan to release the production-ready version in the next SQL Server release wave. We won’t be releasing it in a Service Pack, Cumulative Update, or other form of update for SSRS 2016.
When will we have a production-ready version?
We’re targeting availability in mid-2017.
That makes it sound like they’re pushing it to coincide with the vNext release.