Just posted that in IRC, thought it's worth putting here. My personal idea of the goals for GStreamer are these:
0.8 is about reading and playing every media file on earth without crashing. 0.8 is about reusing pipelines, too.
0.10 is about defining what you may and may not do, making calls signal errors if you do wrong stuff and make everything else not crash. 0.10 is about writing testcases that try all that, too.
1.0 is then about figuring out if everything works like it should and change where it's not
1.2 is about fixing bugs for the GStreamer renderman replacement, the new kernel module doing the netcode with gst and those Cubase replacements based on gst.