Windows Core OS is, of course, a modular, processor-agnostic Windows kernel designed to be paired with so-called Composable Shells. While many shells have been cancelled, the discovery of the test game suggests GameCore is still going strong.
Assuming that Microsoft is planning on using Windows Core OS as a common OS across all of its products, it looks likely that future Xbox consoles – perhaps even starting with the Xbox Series X – would run using a Windows Core OS-based core.