I have a beta release of the upcoming SP version posted now to the download site.
The documentation is not complete yet, but most of the "front matter" material on installs, upgrades, the release notes, etc. is baked enough for testing.
Only the Windows version is packaged because the only inquiries so far have been from people willing to test it there, and the most critical need is for testing the new IIS module. The beta is versioned 188.8.131.52. We will bump the fourth digit on any subsequent releases, though upgrades from the beta are not officially guaranteed to work.
I can probably get test packages built for Linux later this week but likely won't bother unless somebody actually plans to test it in earnest, as it's time consuming.