GPL and AGPL allows you to add more clauses to the license if they don't clash with any existing ones. The FSF should certainly share some guidelines on how we can include and extend the license through an additional "anti-ML / anti-AI" clause.
Even without this, in terms of copyright, since Copilot doesn’t do what your public code does, and it only uses your code to train, it is a transformative use, and would be fair use. It’s possible that a court case will find otherwise, but I think that’s unlikely. The only case I think it will become disallowed, is if Congress passes a law about it.
If Congress does pass such a law, GitHub’s market power in this domain only goes up, since the EULA gives it the covenants.
Unless you can reproduce a substantial portion of a repo, I think it’s going to be an uphill battle to argue it isn’t fair use. Though I suspect Copilot’s suppression feature will make doing so impossible.
Either way, the whole copilot thing smells of 'the issue of copyright infringement is more copyright infringement' to me.
(And I don't see why we cannot add a clause saying that the source code is only meant for human developers and use of the source code in any machine learning system or to train any AI systems is prohibited without explicit case-by-case permission).