I've made use of those even recently. Even if they're not used much now, it's potential future-proofing. And I've written tools that manage content and read these values to organise pages in a series.
yah, rel links are still usuable at least for machine-read purposes, if not the old 'back', 'forward', 'up', type site navigation links that browsers used to display if those were present in the document.
Who knows, maybe someone who works on Chrome or Edge or Safari is reading this thread and will talk to their higher-ups about using it somehow. (Wishful thinking?)