Are there any plans regarding the gstreamer backend to gstreamer-1.0? This discussion has been raised a few days ago in openSUSE devel; since MATE is also a consumer, this ends concerning me also.
My personal belief is that gstreamer-0.10 will probably be around for 1 more cycle, so we're cool. But at some point people will have to migrate.
When does the last "cycle" end? This will determine whether or not the fixed gets squeezed into 1.6 or pushed back until 1.8.
One cycle currently (life-time) is 9 months counting from September, though the freeze will end up some time earlier; I flagged this as RFC (Request for Comments) just to havy any idea. The next release of openSUSE will have most likely GStreamer 0.10 and 1.0, so we're cool.
This is a bit tricky because mate-media's gst-mixer uses gstmixer API, which doesn't have any replacement in 1.0. One option would be to just drop the based gst-mixer and use pulseaudio.
Fixed with migration to libmatemixer, thanks to @mratajsky