Hello :)
seeing the list of things mentioned in this repo makes me thing that we have similar goals.
I've been working for the last few months on Avendish, a C++ library which is able to define media objects that can trivially be compiled against various media systems & APIs such as Max, Pd, etc. , as zero-runtime-cost abstraction (and very low compile-time cost ; the full test suite which builds ~500 different objects being built compiles in 3 to 7 minutes on GH actions depending on the compiler used).
In particular, it is able to express audio/midi processors but also message-based objects and more recently GPU based objects and is to be used as the plug-in API to https://ossia.io ; the sequencer I am working on.
The issues in the repo: https://github.com/celtera/avendish/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc list all the interesting media systems I could find - my short term goal is to port at least one effect of each of those to show that this is possible and makes things both easier and more cross-platform/system.
So if at any point you wish to collaborate this could lead to interesting things I believe!