Comment # 3 on bug 1175922 from Christopher Yeleighton

The solver offered me to resolve the blacklisted dependency by not installing
GNUstep GUI, which would really break GWorkspace.  The minimum damage path
would be to install GNUstep GUI without Xserver, and that path was not given as
an option.

I confirm that GNUstep GUI does not require Xserver to be installed.  Neither
does any other X11 UI client.  They only need a valid display to connect to.