Today I'm releasing an alpha version of gstreamer-media-services, which you can test and report possible bugs. Here you can download it, is not so usable, but you can check how is going the project's idea. Just take care with your testing video and audio files, program is not handling overwrite cases!
I've been talking with Stefan and I'll probably change to implement the gstms core (gstms.py) in C language, to integrate better with gstreamer. I'm just thinking how can I do this, and for now I'm seriously thinking in do it as a gst bin, like decodebin and playbin. I made a diagram of how this could be, profile_diagram, but not sure how could be this XML data profile in sink pad. Probably it's better as a property, but I'm not sure if I can use xml data as gobject property.