This is such a tectonic shift for what the concept of media even means that any assumptions are on uncertain ground.

The courts could find that it isn't possible to sign away these rights. There are many other rights that the law does not permit to be signed away for much more tame reasons than "enables further creations of 'your' work (or in the case of actors, literally 'you') not only without your actual involvement, but even long after your death". I would expect that it at least comes with a time limit. "Artists can sign a license to use these rights but only until their death + 10 years, after that the licensee can't use anything trained on their work. Artists also have an unrevokable right to cancel the license at any time with 90 day notice." might be one possible outcome.