AFAIK, this is the standard VST way of doing things - all MIDI input is processed in blocks in parallel to audio input, and then forwarded along the processing chain. MIDI plugins always get a buffer-load of MIDI commands to process, just like audio plugs get a buffer-load of samples to process - in fact, there is no architectural difference between MIDI and audio plugins - they are just plugins that process their input in chunks of “sample buffer size”.
Every MIDI command received or sent also has a “sample offset” timestamp within the audio buffer, so MIDI plugins are supposed to process a whole buffer at a time.
It looks like this mechanism is one of the key reasons for the sample buffer quantization.
Cheers,
Torsten