My guess is that MS and Apple are both slowly trying to steer their ship in the same general direction as ChromeOS: a stable, locked down OS that runs applications in dedicated sandboxes/containers/VMs. No longer does the OS need to provide the same "shell" to those applications. You don't need a library-based wrapper to the syscall layer. The paravirtualized hardware is the new syscall layer. You can wrap whatever OS interface you want around that in order to support different kinds of workloads. Games can run as close to the system as possible. Workloads destined for the cloud can run in a Linux environment. Instead of being intermediated by clunky VM kit from third-party vendors, they'll provide a lot of it themselves to optimize performance and ensure adequate security between environments in a user-friendly manner.

By making the virtualized hardware the "glue", they can avoid the GPL/copyleft infection of their commercial OS, while supporting different kinds of developer experiences.