regarding note control: I was wondering if it would be helpful to sing through a hardware pitch correction device, and send the corrected audio to the program. That would save the program some overhead of having to pitch correct before it knows where to place the note.

Since that appears to be the major problem... the solution could be fairly simple and avaialble now to anyone who has a voice live or similar hardware for correcting vocal pitch.

Going back to Melodyne...

this wouldn't work for live performances... but for anyone who wants to record midi tracks using their voice as MIDI controller, Melodyne would offer several advantages:

1) it could pitch correct the voice automatically If you are going to send the notes to an instrument patch, most instruments are naturally more perfectly intonated than the human voice. Pitch correcting would increase realism.

2) you could use melodyne like piano roll to experiment and change your track after recording it

3) Melodyne can create all kinds of harmonies from a melody

4) Melodyne also provides other editing tools to fatten up or slim down a note, extend it, shorten it, slide into it, add or subtract vibrato, split it into multiple notes, change key etc etc

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0