is it possible for RNBO to send/receive data between exported AU or VST plugin instances?

RNBO system can only export what you get in the RNBO patcher. If you wanted to send data from within a RNBO to outside of it, you'd need to add something more.

You could use plain C++ to get your own communication protocol between whatever you want to and combine a C++ export with your own C++ to a framework like Juce to compile your VST/AU.

This is a whole work outside of the RNBO boundaries, by the way.

thanks for the info julien, i basically figured as much! just out of curiosity (and since i'm imagining there might be others interested in pursuing something similar)... do you have any idea on best practice for creating such a C++ communication protocol? i've not yet programmed in C++, but i do have programming experience in other languages, so i'm imagining this could be achieved using some shared / global variables between plugins. are you aware of any resources dealing with C++ communication within the context of a DAW plugin architecture? i'm happy to do the research and perhaps share code if i'm able to deal with this successfully.