They should not have released it without a much longer open comment period, if they expected anyone else to implement it. VP8 had barely just come out of hiding from a private company and hadn't been reviewed.
I have known the author of WebP (he previously worked on XviD) and I'm pretty sure it was his pet project.
The Windows "Photos" app doesn't support webp, at least not without an extension, so it doesn't associate the file extension with the app. Chrome can display these photos, so it registers the webp file extension.
https://css-tricks.com/webp-image-support-coming-to-ios-14/ https://caniuse.com/?search=webp