I have no idea why gtk-engines-kde4 was dropped from the tree but all my gtk apps look now horrible. Any hints?
You can use x11-themes/gtk-engines-qt to have Gtk2 apps use your current Qt4 style, or rebuild x11-libs/qt-gui with gtk USE flag to have Qt4 apps use Gtk theme. The latter will make Gtk2 and Qt4 apps look nearly identical, but it may be tricky to set up, so be careful when reading post install emerge messages.