@tristanC also pluguzu is inspiring me to think about porting my "livecode DSP in C" thing to other environments than standalone (optionally JACK-enabled) application.
maybe a Pd external could be the first target, because I'm familiar with that environment. have some ideas for using dlsym() to look up functions for inlet messages too; the tricky part (apart from the threading and race conditions etc) will be supporting accurate timing using Pd's notion of time.
And then a Pd-external version of pluguzu would be fun too, for pattern coding + dsp coding in the same thing.