On one hand this is impressive, and I've been wondering when something like this would appear. On the other hand, I am -- like others here have expressed -- saddened by the impact this has on real musicians. Music is human, music theory is deeply mathematical and fascinating -- "solving" it with a big hammer like generative AI is rather unsatisfying.
The other very real aspect here is "training data" has to come from somewhere, and the copyright implications of this are beyond solved.
In the past I worked on real algorithmic music composition: algorithmic sequencer, paired with hardware- or soft- synthesizers. I could give it feedback and it'd evolve the composition, all without training data. It was computationally cheap, didn't infringe anyone's copyright, and a human still had very real creative influence (which instruments, scale, tempo, etc.). Message me if anyone's still interested in "dumb" AI like that. :-)
Computer-assisted music is nothing new, but taking away the creativity completely is turning music into noise -- noise that sounds like music.