Gabe Aul said on Twitter that Microsoft will release Windows 10 Build 10130 to members of the Insider Preview Slow Ring. He did not give a date, but noted that just one blocking fix is preventing the release. This build was released to Fast Ring users last week and had three known issues. Since then, two were patched via Windows Update, leaving just “Flyouts from Taskbar fail to fly out.” Presumably, this is the issue that they are hoping to fix before pushing the build to Slow.
When the update is released to Slow Ring, it is accompanied by ISOs that can be used to clean-install a PC up to that point. While this delay is to force a segment of users to test the in-place upgrade functionality, I expect this also keeps enterprise evaluators on builds that are more polished. Installing Windows from an ISO might not convey the quality-difference of any two neighboring builds like selecting branches in Windows Update would subconsciously portray.
Microsoft seems to be at the merge and polish stage of Windows 10 development. Builds should start feeling more clean than new as the days roll forward toward July 29th. Major new features are probably going to be done in branches for later releases, similar to what we would consider “service packs”. That's just my assumptions, though.