Honestly, couldn't they just adapt WEBP for it? It's basically just an RIFF container with a VP8 key frame. Then again, it's WebP, and there's no need to bloat that thing anymore.
Edit: Nevermind, I see. Going by the document, it's meant to be an exact mirror to HEIF, but for AV1. Some interesting features too.
> HEIF is a visual media container format standardized by the Moving Picture Experts Group (MPEG)
So corporate politics will surely prevent it from happening. That being said I did file a bug report:
https://github.com/nokiatech/heif/issues/46