While I don't want to prolong the login screen thread unnecessarily, now that *hopefully* it's concluded I wanted to reply to this briefly.
On Wed, 2013-03-20 at 14:02 -0700, Adam Williamson wrote:
It was expected that you could just swap out DMs (like skvidal thinks is still the case) and everything else should just deal with it. The system-config-* tools were part of Fedora and used across all desktops - it didn't matter what desktop you ran, you used system-config-keyboard and system-config-display and so on.
It's not just about the client though - several of these tools were designed for more "enterprise" use cases, like system-config-httpd. At the moment as far as I'm aware the current direction is that gnome-control-center will be focused more on things that matter to client ("desktop") systems.
I think other desktops still think of things somewhat in those terms, but GNOME definitely doesn't: GNOME wants its own stack, almost top to bottom.
It's difficult to speak of a diverse collection of individuals as collectively "wanting" something, but I think even looking just at those who are the strongest proponents of vertical integration, this is an inaccurate characterization.
But there are real world problems that go straight down the vertical stack, and are easily re-broken if one of the components gets out of alignment (i.e. is swapped with a different package). The init system shutdown versus suspend is a perfect example (covered here http://lwn.net/Articles/520892/ ).
So no one wants a stack just to have a stack - it's about solving problems.