Apple has a history of adding sensors, security chips, etc. a few revisions before the feature they support launches. It’s a really good idea because it helps them sort out the supply chain, reliability, drivers, etc. without any customer impact. It decouples the risks of the hardware project from the risks of the software project.

If things go particularly well you get to launch the feature on multiple hardware revisions at once because the first deployment of the component worked great, which is a neat trick.

Yeah, my iPhone 11 Pro came with the ultra-wideband chip in late 2019, and before the AirTags were released in early 2021, I believe the only thing it was used was for ordering AirDrop targets by proximity. It was clearly intended for the AirTags from the beginning, but it took about 1.5 years before it actually mattered.