OK, first some explanations:

At first look they don’t seem to have sth in common. These are some other facts:

As you may have noticed: THIS IS A WHOLE BUNCH OF BULLSHIT GOING ON! I just wanted to update my Gentoo system and got stucked in some stupid conflicts between the mentioned packets. It took about one day to solve it (after reading lots of forum threads of people complaining about the same thing). Check:

Be sure you read them. They’ve helped me a lot to understand this whole topic. So after all this is how I was able to solve it:

# euse -D consolekit policykit upower udisks
# These settings were set by the catalyst build script that automatically
# built this stage.
# Please consult /usr/share/portage/config/make.conf.example for a more
# detailed example.
CFLAGS="-O2 -pipe"
# WARNING: Changing your CHOST is not something that should be done lightly.
# Please consult http://www.gentoo.org/doc/en/change-chost.xml before changing.
# These are the USE flags that were used in addition to what is provided by the
# profile used for building.
USE="acpi smapi mmx sse sse2 cairo svg -kde qt4 qt3support dbus \
     declarative jpeg png vorbis ogg pulse alsa usb sdl spice gtk gtk3 \
     -gnome-shell -consolekit -policykit -upower -udisks"
#source /var/lib/layman/make.conf

# Set PORTDIR for backward compatibility with various tools:
#   gentoo-bashcomp - bug #478444
#   euse - bug #474574
#   euses and ufed - bug #478318
# eselect profile list
Available profile symlink targets:
  [1]   default/linux/amd64/13.0
  [2]   default/linux/amd64/13.0/selinux
  [3]   default/linux/amd64/13.0/desktop *
  [4]   default/linux/amd64/13.0/desktop/gnome
  [5]   default/linux/amd64/13.0/desktop/kde
  [6]   default/linux/amd64/13.0/developer
  [7]   default/linux/amd64/13.0/no-multilib
  [8]   default/linux/amd64/13.0/x32
  [9]   hardened/linux/amd64
  [10]  hardened/linux/amd64/selinux
  [11]  hardened/linux/amd64/no-multilib
  [12]  hardened/linux/amd64/no-multilib/selinux
  [13]  hardened/linux/amd64/x32
  [14]  hardened/linux/uclibc/amd64
# cd /etc/portage/profile
# cat use.force
# cat use.mask
# emerge -aC udev consolekit polkit
# emerge -pv systemd
# emerge --keep-going --jobs 4 --update --newuse --ask --deep --with-bdeps=y @world

Additional steps to clean up your system:

# emerge -a --depclean
# revdep-rebuild -- -q --keep-going