Honestly, all these points make me feel sick from an architecture point of view. Why cannot groups be applied to the user instantly? Why doesn't system have regular ways to change 'registry' values (sorry for analogy, but /etc is a standard-defined setting storage; I'm a unix guy, ftr). If the kernel team has good arguments against that, why hostnamed is not named privilege-d and not using some system bus to change anything beyond hostname? Is hostname the only thing with such problem, the only gui-configurable system-wide setting?
While being a formally valid solution, it all seems like waste of simplicity and totally uncontrolled design process.
> Why cannot groups be applied to the user instantly?
Good question! I've wondered about this before too, ought to research it.
> Is hostname the only thing with such problem, the only gui-configurable system-wide setting?
Of course not :) Systemd provides a half-dozen similar daemons for configuring things; hostnamed is probably the simplest one of them, so I was trying to justify why so much engineering went into something that looks so trivial: it's because the approach is generic.
The idea is that a non-systemd system could reimplement some of these daemons (or rather, their dbus interface; you could implement them in one executable if you want) - and the parts of a standard control panel application relevant to your system would just work.
While being a formally valid solution, it all seems like waste of simplicity and totally uncontrolled design process.