Dear Andrew,
I think the only way a microkernel OS is going to have anything remotely resembling broad success is if is natively Linux-compatible at both the application and driver level. Few people are going to switch to an OS with limited hardware and application support even if it is more secure and/or more flexible architecturally. Seems like I'm one of the few who sees it that way though. I'm not aware of any similar projects to my own (there are a few natively Unix-like microkernel OSes but none have Linux compatibility AFAIK).
FYI: The microkernel-based OS Huawei is working on internally has Linux compatibility (both from the syscall API and from the drivers point of view) as one of its goals.
GNU Hurd obviously also tries to be GNU/Linux compatible (not on the syscall level, but on the glibc level). Many other microkernel-based systems (e.g. Genode, just to name one) maintain their own adaptation layers for hosting Linux device drivers.
There have been several projects targeting componentization/libification of the Linux kernel over the years. If the one you have mentioned won't be short-lived and eventually gets officially supported by the Linux community (like the rump kernel for NetBSD) then it will be certainly a tremendous help for all microkernel projects.
Best regards
Martin Decky