Long live Comment Saver
There's a plugin called Comment Saver, developed by Will Norris and released in 2008. Until a few weeks ago, it "officially" only supported WordPress 2.8.
I stumbled upon it accidentally while exploring someone's WordPress installation, and to my surprise, the plugin still functioned, more or less.
By "more or less," I mean it worked when the debug mode was turned off. Enabling debug mode caused it to throw some warnings and deprecation notices, breaking comment submission because ...
Never mind, because it's no longer the case, as the issue has been fixed. Besides this, the dependency on jQuery was dropped. Now it can be used without adding extra fluff.
The plugin is ready to last another 15 years. Or not.
While I made these small changes, Will put as much effort into it. He dug up the repo and made it available on GitHub. Reviewed the submitted code and added some automation for the release. All this even though he is no longer connected to the WordPress space.
It was understandable that he wanted to avoid the complexity of maintaining E2E tests.
This got me thinking, and it gave me an idea.