Slightly off-topic, I'd love to see an open project for audio plugin specs. VST and AU are managed by private companies and have a history of extremely poor documentation. For anyone who tried to code audio stuff at least once, it's a real pain. Audio is already hard in itself.
(Don't even get me started on the bugs around AUv3…)
It already exists and is called LV2: http://lv2plug.in/ ; you may be interested in http://lv2plug.in/gmpi.html
LV2 at least has units, so you don't need to use some arbitrary rule to convert your Hz, dB, octave, and other units to a 1.0f > float > 0.0f and then that float maybe into an integer.
Putting aside plugin/processor APIs for a moment, I think platform APIs are even worse. I mean, PortAudio, whose namesake is portable audio, does not include a functioning PulseAudio sink, and doesn't function correctly on most GNU/Linux systems of the last decade.
Note that there exist other bindings for VST in Rust, Java, .NET, Delphi... you _have_ to translate part of the SDK to be able to use it from another language that C++.
In essence this is not different than jVSTwRapper or VST.NET, both of which still exist.
But still, I see no reason to use it over LV2 or even LADSPA.
If you don't like that, GPL is still an option.