Maybe not applicable for the XR platform here, but you could add introspection capabilities not present in Linux, a la Genera letting the developer hotpatch driver-level code, or get all processes running on a shared address space which lets processes pass pointers around instead of the Unix model of serializing/deserializing data for communication (http://metamodular.com/Common-Lisp/lispos.html)

You can do that on Linux today with vfork.