The release, earlier this month, of a preliminary version of Windows 10 that was not planned until 2020 was a bit strange. At the time, Microsoft had vaguely said that it was because of features that "required a longer period of time" without any indication of their nature.
Mary Jo Foley, well connected, tells a different story: this publication is actually a consequence of the passage of part of the development of Windows Azure group.
The essential parts of Windows (kernel, file system, network stack, hypervisor, security subsystem, etc.) underlie a wide range of Windows variants, including Windows 10, Windows Server 2019, HoloLens, Xbox One, and Azure. According to Foley, Microsoft releases two versions of these core components each year in June and December. The different variants of Windows are based on these dual versions.
The latest versions of this kernel focused on the requirements of Windows Server, Xbox, and Windows 10, so the Azure team did not feel the need to aggressively monitor and upgrade to each new internal release. Instead, the team runs an older version. But it is the development of these same essential components of Windows that have been moved to the Azure group. As a result, Azure's needs will become more important priorities, and it will be in Azure's interest to keep abreast of each new version released in June and December.
This means, however, that Azure must catch up and, apparently, this has somewhat altered the release schedule. The update Windows 10 April 2019 is almost there, built on the internal version of December 2018. Normally, this work would then be stabilized and integrated in a version of June 2019, which would have taken the code name Vanadium, this version being used as a foundation for the development of Xbox, Windows and Windows Server in the second half of the year. But this year, the publication of June 2019 is ignored. We will still have a feature update for October 2019, but it will also be based on the December 2018 release. The main Windows platform will not see an internal version (code name Vibranium) until December 2019.
This would explain why the 2020 work started early – because that's where the next version of Windows will come from, so it's what needs to be tested. The way this really helps the Azure team is less clear, but I suppose that removing the June version would give the Azure team more time to synchronize with the December 2018 release and align its platform. form on the rest of Windows. From that moment, things should resume, with an internal version of June 2020 with the code name Manganese.