Mach was created at CMU, and later development moved to the University of Utah. This work became the basis of the NeXT operating system, which then turned into Mac OSX.
So I'd call this a "viable reality".
PS -- I think you meant "GNU/Hurd", not "GNU Mach".
Except that in the process, Mach absorbed BSD and became a weird hybrid of the two. I worked on Mach as an undergrad at CMU when the BSD server was intended as a temporary expedient to port the Unix userland tools quickly. Instead, it made its way into the kernel.
So I'd call this a "viable reality".
PS -- I think you meant "GNU/Hurd", not "GNU Mach".