Both mate-desktop-environment and xfce-polkit require dbus-x11 to be installed to work, and so they should include it as a dependency.  It may be that xfce-polkit should also carry consolekit2 as a dependency.  Certainly I like xfce-polkit being separately packaged because the dbus/consolekit requirements are then isolated from xfce4 itself.  Some of this may also be true for lxplkit and polkit-gnome as well, but I had not tried these desktop environments on alpine yet.