I'm not sure that it does what you want, but glame is designed with the
engine and gui completely separated. The control language for glame
networks is guile. It has much of the core for a full sequencing system
(tone generators, ladspa plugin support), but no midi support. Domage.
I have always been interested in guiless synthesizers for reasons that
probably have a lot to do with why I'm a devoted ecasound user for my
multitracking needs.
Bill