Ideas

Bindings for scripting language, this would make it possible to interactively build pipelines.
Wrappers for LADSPA and LV2 plugins, probably as SPA plugins so they can be loaded with the SPA module directly.
Dynamic format updates are not very well worked out. (WIP)
Decoders, demuxers probably based on FFMPEG would allows us to make playback pipelines.
PulseAudio
JACK
Think about latency. We would want to do automatic latency correction (unlike JACK) to align related streams.
Make a Wayland server module that you can connect to with an application and it creates a node with the contents of the application. Probably needs some event input as well to make this useful. Once that works, make a compositor node that takes N inputs.