just a small mention of an idea ... i know of at least one (undercover) LADSPA plugin right now which maintains "global state". rather than every instance of the plugin being 100% independent, every instance is "connected" to the global state. this makes it possible to do some "across the entire mixer" tricks that would be impossible with the "every instance is independent approach".

but yes, in general, i would want to echo fons' point that doing this kind of thing *inside* ardour is crazy. 2.8 contains, in addition to session templates, track templates. this means that you can, for example, get an ambisonics session template established, along with 1 or more ambisonics track templates. these templates will include the routings to (for example) ambdec or some other multichannel-aware application. this then makes it almost trivial to recreate complex session setups each time - start with the right session template that routes audio via ambdec or whatever new magic fons comes up with, then add tracks/busses from track templates that already define the correct output wiring.
 
the multichannel panner in ardour should be ignored. i'd like to find a sponsor to support the development of a VBAP-based replacement. after talking to several multichannel/surround people in berlin, it seems clear that both ambisonics and VBAP have their roles. the ambisonics setup is better done via ambdec because of the number and complexity of the parameters, but VBAP could be done quite nicely inside ardour. its not going to happen without someone raising a relatively significant amount of money, or somebody else doing the work.

--p