On October 13th, TO posted an update to the Doom 2 Project on OCRemix, saying:

“The mixerlist has been culled due to inactivity. The mixers that were on those tracks can still be a part of the project, so long as they submit me a final version. I won’t sit anyone on the track unless I’m sure I’ll get a final version from them.”
You can see what tracks are available and how to join the project here: http://www.ocremix.org/phpBB2/viewtopic.php?t=71824.