Comment 5 for bug 879943

I don't get the approach too. It's nice cause it splits GUI and back-end. The dbus service is in software-properties-common:

$ apt-cache rdepends software-properties-common
+software-properties-common
Reverse Depends:
  ubuntu-desktop-next
  phablet-tools-citrain
  ubuntu-touch
  phablet-tools-citrain
  cloud-init
  ubuntu-touch
  ubuntu-desktop-next
  software-properties-kde
  phablet-tools-citrain
  software-properties-gtk
  cloud-init

It seems not that many packages use the service. (ofc software-properties-kde does)

I also think there should be a watcher or a check. Or at the very least let the GUI represent the same sources as the back-end.