Microsoft has pushed a test build for Windows 10 20H1, which is scheduled to be publicly released around April 2020. For context, we are currently on Windows 10 18H2 and Windows 10 19H1 is expected to ship in a couple of months (~April 2019).
Microsoft still plans on shipping Windows 10 19H2 around October 2019.
This decision was met with snark from some of the more prominent reporters on Microsoft and Windows. One issue that was raised is how the rings will be handled going forward. Currently, there does not exist a branch that contains 19H2. It seems likely that “Skip Ahead” will never drop back to 19H2, especially since rolling back from a preview build is generally unsupported. Will Microsoft continue to have “Skip Ahead” be two builds out, “Fast” be one build out, “Slow” be at most one build out, and “Release Preview” be incremental on the current build? Or will “Skip Ahead” kind-of roll back to “Fast” once the latter catches up and they no longer need to have a feature that requires an abnormally long testing branch?
As for the changes? Not a whole lot. One that stands out is a seemingly innocuous “updating the name of the Windows Light them to be Windows (light)”. This sort-of suggests themes that will not be Windows. I could see some sort of interface or theming update taking an abnormally long time… although I somewhat doubt that is the mystery big feature.
On the other hand, it must be something that Microsoft wants actively tested. Whether that’s automated (via telemetry on a wide array of computers) or through direct feedback from their users will need to be seen.