You can express the “lossless frames” aspect of GIFs today in existing video ways supported by MJPEG, H.264, H.265, or AV1 today.
AV1 image sequences are meant for sharing an album of stills, and are not a convenient shortcut for this.
Feeding a sequence of frames into `aomenc --lossless=1` should, assuming everything else is working correctly.
I believe looping is not currently a property that you can readily set at the codec level, which is perhaps the most critical missing feature of AGIF when considering codecs.
Perhaps focusing on the “loop” flag’s presence/absence and whether it’s honored by browsers would most usefully serve the post-GIF world?
Should AGIF continue to autoplay when in more efficient other formats it may not?