okabe ~ # emerge -uDU --ask --keep-going --with-bdeps=y @world

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

Calculating dependencies \

!!! Problem resolving dependencies for net-misc/networkmanager from @steam
... done!

!!! The ebuild selected to satisfy "net-misc/networkmanager" has unmet requirements.
- net-misc/networkmanager-1.14.6::gentoo USE="bluetooth consolekit dhclient elogind introspection modemmanager ncurses nss policykit ppp wext wifi -audit -connection-sharing -dhcpcd -gnutls (-iwd) -json -ofono -ovs -resolvconf (-selinux) -systemd -teamd -test -vala" ABI_X86="(64) -32 (-x32)"

  The following REQUIRED_USE flag constraints are unsatisfied:
    at-most-one-of ( consolekit elogind systemd )

  The above constraints are a subset of the following complete expression:
    iwd? ( wifi ) modemmanager? ( ppp ) vala? ( introspection ) wext? ( wifi ) exactly-one-of ( nss gnutls ) at-most-one-of ( consolekit elogind systemd )

(dependency required by "@steam" [set])
(dependency required by "@selected" [set])
(dependency required by "@world" [argument])