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

Calculating dependencies ...

!!! Problem resolving dependencies for =gnome-base/gnome-control-center-49.9
 done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=gnome-base/gnome-control-center-49.9" has unmet requirements.
- gnome-base/gnome-control-center-49.9::gentoo USE="X bluetooth cups geolocation gnome-online-accounts ibus -debug -elogind -kerberos -networkmanager (-systemd) -test" INPUT_DEVICES="-wacom"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( elogind systemd )