It is a good idea.
I think there are manifold ways around the copyright question.
But this is, IMHO, far too ambitious a project to succeed.
It's not really not a question of me being a naysayer, and it is true that advertisements for proprietary products don't delight me, but here it's an interesting idea.
For the simple reason that there is no deterministic algorithm that can possibly achieve more than the most superficial of results. And, even those results? Of what quality?
For any meaningful output, the machine would have had to have been force-fed an enormous amount of material. And what of the results?
HOWEVER, I do like the idea, and perhaps like some others here and elsewhere, rewriting and reconfiguring scores has been a big part of my own education.
I'd like to see some results, though: much like the fable of automated automobile driving, nothing would make me happier than to see promising results.
The (i) Why? has been established, the (ii) How? is a mystery, but not important, but it leaves open the question of (iii) What? And in what way?
There's just not an ontology of standard notation and the way these notations are interpreted, so it's going to fail in the same ways other automation attempts have.
I wish it were not so, and I don't claim that's a priori true, but I'd like to see a good example in action. A prototype, if you want.
There could be a value in having a kind of stochastic, John Cage style of "notation terminator" roaming around, ready to transform scores into some variations.
I think that's the best outcome, and I would like to use such a program.