From another place in this thread:

As OpenJDK has switched to time-based releases, we no longer plan releases based on features. When a feature is ready, it is merged into the mainline and released in the following release. We never commit to a timeline, but I would say that the probability for fibers to land in one of the two releases next year as quite high. Of course, we release projects gradually, and it's possible that some planned fiber features will not land in the first release, or that the performance in the first release will later be improved etc. However, early access Loom binaries (with API still very much in flux) are expected in a month or so, with the intention of gathering feedback on the API. The decision on when fibers are ready to be merged will greatly depend on that feedback.