Since qt4 separated much of it's functionality into separate shared libs, it is now possible to create console (ie, non-gui/x11) qt4 apps. In this case, installing the existing qt4 pkgs with it's dependancies on xorg-x11 would be largely wastefull. For example, SuSE has a qt(4)-x11 subpkg.
So, what to name the "gui" bits... qt4-x11, qt4-gui? Atm, I'm leaning toward qt4-gui
Turns out most other pkgs use -x11 for this, -gui usually implies an gui *app*.
* Wed Jun 28 2006 Rex Dieter <rexdieter[AT]users.sf.net> 4.1.4-4 - x11: split-out gui(x11) from non-gui bits (bug #196899)