Having done a bit of digging, and perhaps some soul searching, it seems that Poettering, and others, think that a tightly coupled system is the only way to build a OS.
This because they see generic distros, like Debian and Gentoo, have in effect dug themselves a hole thanks to the number of permutations involved in packaging (though with Gentoo being compiled by user/admin rather than distro maintainer it may not be fully correct to include them).
But to go from saying distros may have bitten over more than they can chew, to saying that everything between kernel and desktop needs to be a tightly coupled whole is quite the leap.
Yes, distros can be built to be highly specialized, and has been so since the early days. But that is not an excuse for making the software that goes into making a distro tightly coupled.
Also, way to much of what is happening above the kernel is happening from the desktop environment (Gnome in particular) down.
Take dbus for instance, it balks at talking across user accounts. But if it was amended to do so, user accounts become sandboxes.
But instead we get the whole rigmarole of cgroups and namespaces, managed by systemd.