The reason those have to be kept in sync is simply because you don't want to run fsck on a filesystem that was built with a newer kernel that possibly has datastructures that your fsck (or other filesystem aware utility) accesses directly without going through the kernel. Essentially such programs re-implement a bunch of kernel functionality because they access file systems that are not currently mounted.
Systemd on the other hand (in the case at hand) replicates the functionality of another user process that we already have, know how to use and have hardened over many millions of hours of use. That seems folly to me, it duplicates functionality, makes troubleshooting harder and increases the size of the codebase without actually improving anything.
What's next? The framebuffer? Keyboard interface? TCP stack?
There are no really hard reasons why those could not be user programs. It's fine with me if we make linux a micro kernel but let's do that in a way that we do not need to revisit the last decade or so of security issues and ill thought out interfaces. Once we start to need things like DBUS and X in order to bring up a server we've really lost the plot.
I'm afraid so: http://lists.freedesktop.org/archives/systemd-devel/2013-Nov...
A userspace replacement entitled kmscon has already been around since 2012, by David Herrmann. It's a totally separate project.
consoled is a minimalistic fallback done by the same person. I'm not sure if it really needs to exist, but replacing CONFIG_VT in of itself isn't bad. Most people will probably still have kmscon primarily.
Linux develops fewer things this way than the BSDs typically do, outsourcing a lot of userland to other projects like GNU, but it doesn't literally develop only kernelspace code. Imo it's generally an improvement; the situation with trying to get things like cgroups to work together with process management previously was terrible.