I would love something like that, except that I play the melody, and it produces proper 3-4 part accompaniment, preferably in good baroque style. Extra bonus if it could also write it into a file in a format suitable for music editing programs.
The closest we've had to realtime orchestration around a melody in the "real world" is probably arranger keyboards though your left hand is still responsible for the chord progression itself.
[1] - https://en.wikipedia.org/wiki/Microsoft_Research_Songsmith
Some details: https://shop.chessbase.com/en/products/ludwig_3_engl
You can still download it for free: https://www.heise.de/download/product/ludwig-58854 (Heise is a renowned German publisher, nothing shady)
I am still waiting for something like this based on generaitive AI.