The HURD distribution contains a large number of libraries. This was a design decision taken early on, since it was thought likely that as a large number of similar services would be desired, abstracting as much as possible into libraries was a good idea. One of the libraries in the HURD distribution is LibMOM (Microkernel Object Module) which provides an abstraction layer between HURD processes and the underlying microkernel. The intention of this library is that to port HURD from one microkernel to another it should only be necessary to rewrite LibMOM.
However, careful examination of the sources show that none of the components of HURD currently use LibMOM. So the first step in porting HURD to any other microkernel must be to alter the various servers to use the LibMOM indirection layer.