Hallo!
I just have come over the vamp plugins (http://www.vamp-plugins.org) again. It is a plugin system for feature extraction, audio analysis and is used by the Sonic Visualizer, Ardour, Audacity and others ... There already exist many plugins (see http://www.vamp-plugins.org/download.html and the features listed there) and it would be definitely nice to have them in pd.
However, it's also not so straight forward to implement a host, because some plugins need data in frequency domain or in a specific blocksize ...
I made a GSoC page where I described it in more details (http://puredata.info/dev/summer-of-code/VampPlugins) and would be definitely interested in implementing this for GSoC. Anyhow, I don't know if this project might be too small ... maybe it can be also combined with something else ?
LG Georg