Support for the new AVIF image format should be coming to Firefox and Chrome later this year: https://www.zdnet.com/article/chrome-and-firefox-are-getting-support-for-the-new-avif-image-format/
It is a new image format derived from the AV1 video codec that seems to offer a very good quality to file size ratio compared to jpeg and has some advantages over webp such as support for multiple forms of sub-sampling (webp only allows 420); which combined, should prove of great utility on the web and fits in very well with the common high performance association of static sites. https://netflixtechblog.com/avif-for-next-generation-image-coding-b1d75675fe4
Rust support for the codec seems to be in it’s infancy at the moment, but the rav1e encoder and decoder seems to be progressing very rapidly. I imagine the amount of work to add this to Zola at the moment would be very non-trivial, but hope opening a thread might prompt constructive discussion of whether it would be useful and how to go about implementing it if so.