I mean, it’s the same as trademark disputes; legal standards will slowly be cobbled together from statutes, regulations, and random judges setting precedent. “Confusion in the marketplace” seems like a potentially relevant term — accidentally producing a product similar to an existing person’s voice is one thing, but publishing it in a manner and/or context that makes it seem like that person recorded the lines is something else entirely.

Anyway, given how the election is shaking out on Twitter, I have a feeling political usage will spark legislation and precedent far before commercial usage does. But that’s just a plain guess