My random notes about the stuff I've done
I added the Theora support back to ogg-support and uploaded the source packages to extras-devel builder.
I didn’t change the mimetypes though, so all *.ogg files are seen as audio files even though they may contain video streams as well. I quickly transcoded the Big Buck Bunny video to lower resolution ogg containing Theora video and vorbis audio. The Media Player was able to show it although I should have used even lower resolution (and lower audio bitrate).
Comments are welcome.