How about adding the ability to use midi synthesizer vst plugins?
What do you want the plugin to do? For example, if you tried to get Audacity to record your MIDI keyboard or controller, the MIDI data would have to go into Audacity, get converted to sound, play in Audacity, turn around and then come back in again to be recorded. A cousin to recording streaming audio.
And if you got all that to work, somebody’s going to want to overdub and there’s no way to get rid of the multi-pass delays.
No simple task, this.
Maybe it would be possible to choose if the midi track should be played to audio out by using a sound generator or send to a midi controller.
In last case, audacity would be the only software which can play midi and audio files at the same time and synchronized, in case if there is a midi track and an audiotrack in the audacity project.
That would be great!
The current version of Audacity can play MIDI. See: https://manual.audacityteam.org/man/note_tracks.html