Hello,
apart from creating media art which not seems interesting for you, I recently start to use PD as a modular effectbox. Having a meanwhile old laptop with an USB audiobox with no task I integrated it in my studio the oldschool analog way like you would integrate other synths and effects. I started to develop several basic blocks for processing which can be easily connected, the biggest task was to store settings AT LEAST one per patch. I did an abstraction but maybe another approach is more common, maybe someone an idea? I ever wanted to have an Eventide box but now I got something simular and when you look at their editors its actually the same thing. I got real big fun with pitchshifters connected to lfos, another delays and feedbacks. I plan to put the modules online because I believe its a good way to reuse your old computers. You can even create something like a Roland V-Synth when you look on the FFT tutorials and combine it with filters and resonators.
In an artist-in-residency I implemented some synthesis technics, maybe you look at
http://access.lowtech.org/e-gehirn/workshop.html
it shouldnt be so difficult to implement midi. Currently these patches where used on old pcs connected over ethernet. Every instrument is controlled by a stepsequencer, synced by a masterclock broadcasted over the network.
Cheers,
Malte