> I think we can add `DeprecationWarning` for 3.9.

If we add the deprecation warning just for 3.9, would the removal release also be pushed forward? 

> Honestly, we just missed the issue when were prepared for 3.8

Yeah that's definitely understandable, there were quite a number of major changes made in 3.8. It was the first time I saw a deprecation clearly documented in a final release that didn't have an associated deprecation warning. 

As for 3.8, I would like to update the whatsnew entry to add a link to this bpo issue if that's okay, as it does not at the moment. I recently included the entry in a PR that added entries for multiple significant changes for asyncio in the 3.8, but I forgot to include the bpo link (mostly because I found it in the documentation, rather than from the bpo issue).