Now that all branches support blurb, I have added a status check for a news entry. If a PR doesn't require a news entry then simply set the "skip news" label and the status check will then pass. When there is no news entry the Details link of the failing status check points to the appropriate part of the devguide so hopefully some contributors will self-discover the need for a news entry and create the appropriate file without being prompted for it.
I'm going to wait a little while -- probably end of the week -- to verify I didn't botch the code before I make this a required status check like with the issue number check (I've already had to push out an emergency fix once already today so it has validated that waiting is good :) .
And with this I am taking a break from coding new workflow tooling for a little while and switching to feature work for Python 3.7. :)