These are the packages that would be merged, in order:

Calculating dependencies  ..... done!
[ebuild  N     ] x11-themes/gnome-backgrounds-3.20::gnome-kit  15,935 KiB
[ebuild  N     ] gnome-base/gnome-menus-3.13.3-r1:3::gnome-kit  USE="introspection -debug {-test}" 396 KiB
[ebuild  N     ] dev-libs/libgee-0.18.0:0.8/2::gnome-kit  USE="introspection" 0 KiB
[ebuild  N     ] dev-util/meson-0.43.0::dev-kit  PYTHON_TARGETS="python3_4 -python3_5 -python3_6" 1,042 KiB
[ebuild  N     ] gnome-extra/zenity-3.20.0::gnome-kit  USE="libnotify -debug {-test} -webkit" 0 KiB
[ebuild  N     ] media-libs/glew-2.1.0:0/2.1::media-kit  USE="-doc -static-libs" ABI_X86="(64) -32 (-x32)" 0 KiB
[ebuild  N     ] x11-apps/mesa-progs-8.3.0::xorg-kit  USE="egl -gles2" 0 KiB
[ebuild     U *] sys-apps/util-linux-9999::core-kit [2.29.2-r1::core-kit] USE="cramfs ncurses nls pam python readline static-libs suid unicode -build -caps -fdformat -kill (-selinux) -slang -systemd {-test} -tty-helpers (-udev)" ABI_X86="32 (64) (-x32)" PYTHON_SINGLE_TARGET="python3_4 -python2_7 -python3_5" PYTHON_TARGETS="python2_7 python3_4 -python3_5" 0 KiB
[ebuild  N     ] sys-apps/systemd-236-r5:0/2::nokit  USE="acl gcrypt kmod lz4 pam policykit seccomp ssl sysv-utils -apparmor -audit -build -cryptsetup -curl -elfutils -gnuefi -http -idn -importd -libidn2 -lzma -nat -qrcode (-selinux) {-test} -usrmerge -vanilla -xkb" ABI_X86="(64) -32 (-x32)" 6,655 KiB
[ebuild  N     ] sys-apps/gentoo-systemd-integration-7::nokit  63 KiB
[ebuild   R    ] sys-apps/dbus-1.10.18::core-kit  USE="X systemd* -debug -doc -elogind (-selinux) -static-libs {-test} -user-session" ABI_X86="(64) -32 (-x32)" 0 KiB
[ebuild  N     ] dev-python/pyatspi-2.20.3::gnome-kit  PYTHON_TARGETS="python2_7 python3_4 -python3_5 -python3_6" 0 KiB
[ebuild  N     ] app-accessibility/caribou-0.4.21::gnome-kit  PYTHON_TARGETS="python2_7 python3_4 -python3_5" 0 KiB
[ebuild  N     ] x11-wm/mutter-3.20.3::gnome-kit  USE="deprecated-background introspection kms {-test} -wayland" 0 KiB
[ebuild  N     ] net-im/telepathy-logger-0.8.2:0/3::gnome-kit  USE="introspection {-test}" 0 KiB
[ebuild  N     ] gnome-base/gnome-core-libs-3.20.0:3.0::gnome-kit  USE="cups python" 0 KiB
[ebuild  N     ] gnome-base/gnome-shell-3.20.4-r2::gnome-kit  USE="bluetooth deprecated deprecated-background networkmanager nls -systemd -vanilla-motd" PYTHON_TARGETS="python3_4 -python3_5 -python3_6" 0 KiB
[ebuild  N     ] gnome-base/gdm-3.20.1::gnome-kit  USE="deprecated introspection ipv6 tcpd xinerama -accessibility -audit -branding -fprint -plymouth (-selinux) -smartcard -systemd {-test} -wayland" 0 KiB
[ebuild  N     ] x11-terms/gnome-terminal-3.20.2::gnome-kit  USE="gnome-shell nautilus -debug -vanilla" 0 KiB
[ebuild  N     ] gnome-base/gnome-light-3.20:2.0::gnome-kit  USE="cups gnome-shell" 0 KiB
[blocks B      ] sys-apps/sysvinit ("sys-apps/sysvinit" is blocking sys-apps/systemd-236-r5)
[blocks B      ] >=sys-apps/systemd-197 (">=sys-apps/systemd-197" is blocking sys-auth/nss-myhostname-0.3)
[blocks B      ] sys-apps/gentoo-systemd-integration ("sys-apps/gentoo-systemd-integration" is blocking sys-fs/eudev-3.2.2-r1)
[blocks B      ] sys-apps/systemd ("sys-apps/systemd" is blocking app-admin/openrc-settingsd-1.0.1)
[blocks B      ] sys-auth/nss-myhostname ("sys-auth/nss-myhostname" is blocking sys-apps/systemd-236-r5)
[blocks B      ] sys-fs/eudev ("sys-fs/eudev" is blocking sys-apps/gentoo-systemd-integration-7, sys-apps/systemd-236-r5)
[blocks B      ] sys-apps/systemd ("sys-apps/systemd" is blocking sys-fs/eudev-3.2.2-r1)

Total: 20 packages (1 upgrade, 18 new, 1 reinstall), Size of downloads: 24,089 KiB
Conflict: 7 blocks (7 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  sys-apps/systemd-236-r5:0/2::nokit, ebuild scheduled for merge pulled in by
    >=sys-apps/systemd-207 required by sys-apps/gentoo-systemd-integration-7:0/0::nokit, ebuild scheduled for merge
    sys-apps/systemd:0= required by sys-apps/dbus-1.10.18:0/0::core-kit, ebuild scheduled for merge
    sys-apps/systemd required by x11-wm/mutter-3.20.3:0/0::gnome-kit, ebuild scheduled for merge
    sys-apps/systemd required by virtual/tmpfiles-0:0/0::core-kit, installed

  app-admin/openrc-settingsd-1.0.1:0/0::core-kit, installed pulled in by
    app-admin/openrc-settingsd required by gnome-base/gnome-control-center-3.20.2:2/2::gnome-kit, installed

  sys-apps/sysvinit-2.88-r10:0/0::core-kit, installed pulled in by
    >=sys-apps/sysvinit-2.86-r6[selinux?] (>=sys-apps/sysvinit-2.86-r6) required by sys-apps/openrc-0.35.0_beta1:0/0::core-kit, installed

  sys-fs/eudev-3.2.2-r1:0/0::core-kit, installed pulled in by
    >=sys-fs/eudev-2.1.1 required by virtual/udev-217:0/0::gentoo, installed
    >=sys-fs/eudev-1.3:0/0[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_ppc_32(-)?,abi_ppc_64(-)?,abi_s390_32(-)?,abi_s390_64(-)?,static-libs] (>=sys-fs/eudev-1.3:0/0[abi_x86_32(-),abi_x86_64(-),static-libs]) required by virtual/libudev-232:0/1::gentoo, installed


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages


The following keyword changes are necessary to proceed:
 (see "package.accept_keywords" in the portage(5) man page for more details)
# required by sys-apps/systemd-236-r5::nokit
# required by sys-apps/dbus-1.10.18::core-kit[systemd]
# required by net-im/telepathy-logger-0.8.2::gnome-kit
# required by gnome-base/gnome-shell-3.20.4-r2::gnome-kit
# required by gnome-base/gdm-3.20.1::gnome-kit
=sys-apps/util-linux-9999 **

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by sys-apps/systemd-236-r5::nokit
# required by sys-apps/gentoo-systemd-integration-7::nokit
>=sys-apps/dbus-1.10.18 systemd

NOTE: The --autounmask-keep-masks option will prevent emerge
      from creating package.unmask or ** keyword changes.

 * In order to avoid wasting time, backtracking has terminated early
 * due to the above autounmask change(s). The --autounmask-backtrack=y
 * option can be used to force further backtracking, but there is no
 * guarantee that it will produce a solution.