I've started a thread over on the Audacity forums about the idea of using libpd to make a Pd-patch-based plugin architecture for Audacity. It would be quite nice to make Audacity plugins using Pd. Weigh in on the discussion over there:
http://forum.audacityteam.org/viewtopic.php?f=20&t=42728&p=109218#p109218
http://forum.audacityteam.org/viewtopic.php?f=20&t=42728&p=109218#p109218