A file per news entry seems a bit much, but an optional file per developer would solve most of the problem for those who have a problem with the status quo. Add a directory named, for instance, news.3.4.1. Put in a template with the allowed section headings. Call it something like aaTemplate.txt to sort first. To avoid merge conflicts due to entries for new features in default, quadruple space between headers so the only non-blank context would be the section header above. Developers like me who have a problem with the existing system could copy the file, rename it with their name (terry.reedy.txt, etc), hg add it, and use it for news entries (with extra blank lines to maintain the clean context.

A script could be written to sync the working directory (pull and merge), move entries into NEWS (skipping over blank lines), recopy the template, commit and push.

If I were working on non-Idle code issues, I would seriously consider doing the above with a private, non-repository file in /MISC that I might merge one a week or so.

Someone objected to changes that result in news entries being out patch push order. This is already not a rule because the devguide mentions inserting new items at random positions to avoid conflicts due to another commit. Also, News items are frequently pushed sometime after the corresponding patch. I don't know if this is because people forget or because they want to isolate any hassle with a news conflict. In any case, the News entries are not necessarily time ordered now.

From a user perspective, having library news items sorted by affected module, with code, doc, and test changes collected together, would generally be more useful.