The plugins do not have slots. It is needed for proper testing in overlays new 0.11. Should be done before 1.0 comes out. It will possibly break some stuff, so two versions of gstremer could be needed. Reproducible: Always
I'm pretty sure SLOT is only forgotten for gst-plugins-bad and its splits. Was going to take care of it while doing next bumps (and hence going over all -bad ebuilds anyway, to modify their older versions slots as well).
As a random general additional comment - note that current SLOT=0 _is_ also a SLOT. It's just a very counter-intuitive naming and different in -bad accidentally to the others, which are already 0.10, so we don't want other ebuilds to slot depend on that, but on 0.10 instead after slotmove.
I believe this was fixed by Mart on September 7.