Both authors saw PEP-649 as a solution, with no need to raise alarm bells. If you follow the discussion of the last proposal, you’ll see that it’s acceptance is

Both authors saw PEP-649 as a solution, with no need to raise alarm bells. If you follow the discussion of the last proposal, you’ll see that it’s acceptance is now in doubt, and it’s inclusion in 3.10 seems unlikely. Both authors have been active in that discussion. The issue is not that they had no warning, it’s that the proposed solution is being pulled out from under them.