Yeah there were actually a couple of projects along this line at various points, but they always suffered in various ways from not being well integrated into th

Yeah there were actually a couple of projects along this line at various points, but they always suffered in various ways from not being well integrated into the system. What you really want is for the colocated kernel to have first class access to some basic things about the primary kernel (like file systems -- including page caching and networking) so they're not going through an expensive and awkward translation layer. Cygwin and things like colinux exist on opposite ends of that awkward divide, but something officially supported by the OS could maybe straddle it better.