Is there going to be an avalanche of code that is legally in the public domain, going forward?
The more interesting question: will companies need to document human contribution to defend copyright claims? That might accidentally improve code review practices.
Even if AI output isn't copyrightable, could you really argue a solid case if I taint random parts of the source code with my own isms? Which this is something I do, I don't care if the AI generated portions of my code base are copyrightable, perhaps my licensing is not valid for those portions, but throughout my code is going to be parts I hand crafted or patterned out because the AI just can't get it right. Those snippets are just proverbial land mines in waiting for a copyright infringer in waiting.