I also have high hopes for Guix, and in fact there is a gsoc project to port Guix to the Hurd. Guix tries to empower the user, a goal shared by the Hurd. They are a perfect match.
I do not believe that it is easy to provide the Mach IPC interface in the Linux kernel. The IPC mechanism is tightly integrated into the thread switching and scheduling systems.
Furthermore, I do not see much benefits in doing that, the main point would be drivers, which we want to run as a userspace process anyway. And we are doing that using the DDE framework. Rump is interesting, and it wouldn't even be that hard. It just lacks someone actually doing it.
What people don't realize is how compatible the Hurd is. We are shipping the glibc. Debian/Hurd contains ~80% of the software that is found in Debian/Linux. We have Firefox. The other day I deployed two Django sites on my Hurd development server to work out some issues I had with the Apache configuration I had on the production system. I was curious how it would go. All the Python stuff worked out of the box, I merely had to select a different Apache mpm module, because the default didn't work. Need to rescue a box? Append "init=/bin/bash" to the kernel command line to circumvent sysvinit.
Other microkernel based systems might have more ambitious goals, but many of them sacrifice compatibility to reach them. Some aspects in POSIX are hard to implement in a distributed fashion, for example fork(2). But what good is a fancy system if it requires a huge effort to port applications to it?