[Spivak]

If you mean what Wayland literally calls "staging" it means that compositors should adopt it now, it doesn't mean pre-release. Once multiple compositors implement the protocol it can become stable.

[holowoodman]

Staging still means it is untested because not widely implemented. And still unsupported by the majority of compositors. So basically still unusable.

Also, "can become stable" is a very rare thing. Only a single-digit percentage of staging ever became stable.