What I said was not restricted to retroactively applying a license. HN cannot automatically apply a license to new content either. It was at first unclear to me

What I said was not restricted to retroactively applying a license. HN cannot automatically apply a license to new content either. It was at first unclear to me how you meant for HN to apply the license. It seems clear now that the intention is that users would have to explicitly grant HN permission. This is good, and I'm all for it. It does need to be clear though that users are explicitly granting permission. And I agree with others that an opt-out is definitely a good idea.