You probably couldn't get it to run on bare metal, what with I don't think Mach handling message-signaled interrupts for PCI, on top of the lack of USB and sound for desktop functionality. It's strictly developed and used in virtualization currently, and the motivation for rump kernel integration is to finally escape the hellish circle of that and relying on old NetDDE drivers, perhaps finally making it an everyday OS.
On the other hand, it is stable enough to serve the Hurd wiki. In addition, it has ~81% of Debian building, it can run Xfce and Firefox... not bad. It's much more than MINIX 3, which is solid but lacking in packages.