app-emulation/emul-linux-x86-medialibs should provide gst-plugin-scanner. Gstreamer try to load plugins with gst-plugin-scanner and since there is only ELF64 version in system it fails to load 32 bit plugin. Sample error when launching 32 bit app on 64 bit system that use gst (app-emulation/emul-linux-x86-gstplugins and app-emulation/emul-linux-x86-medialibs are both installed): (gst-plugin-scanner:3839): GStreamer-WARNING **: Failed to load plugin '/usr/lib32/gstreamer-0.10/libgstfreeze.so': /usr/lib32/gstreamer-0.10/libgstfreeze.so: wrong ELF class: ELFCLASS32
The emul-linux-x86 packages have been removed.