I don't think it would be necessary to be in the law. The composers don't have to sign an assignment of rights to work with a music publisher, and they don't even need to work with a music publisher because some people do their own business by themselves.
There's nothing in the law that stops what we're discussing being effective in a contract. You could say that after 35 years the copyright would go back to the composer. That's already possible to do if we wish to do it, and I think there's a difference between the ownership and the remuneration. I think what's important for copyright owners is the remuneration side, and that's what we should focus on. How much value can we give to copyright and how much money can we bring to the music industry?
I'll end by saying that music publishers have catalogues of copyright that bring in steady streams of revenue, which are used to reinvest in new talent. We have to keep that in mind. That's the business model of music publishers.