That's not a replacement nor a competitor for the popular "JPEG" format. The only commonality here is that it's coordinated by the Joint Photographic Experts Group.
You'll never see JPEG-XS images stored on disk or sent over the web. This is a special-purpose format for video signals on the wire (e.g. for transmission between your graphics card and a 4K monitor). Currently if your cables don't have enough bandwidth for the full uncompressed RGB signal, you get lower FPS, or lower bit precision, or subsampled YCbCr. This is an attempt to make something a bit smarter and apply cheap nearly-lossless compression on the fly instead.
You'll never see JPEG-XS images stored on disk or sent over the web. This is a special-purpose format for video signals on the wire (e.g. for transmission between your graphics card and a 4K monitor). Currently if your cables don't have enough bandwidth for the full uncompressed RGB signal, you get lower FPS, or lower bit precision, or subsampled YCbCr. This is an attempt to make something a bit smarter and apply cheap nearly-lossless compression on the fly instead.