AV1? It's mainstream already. Lots of hardware supports it and you don't need hardware support for many other cases.

AV1 decode works well enough even on quite old devices, and it has more favorable quality and size, individually or when considering both. I prefer it to h264 (or vp9 or even h265) at this point, and there isn't a particular need for hardware decode to benefit from it. On Youtube (probably the biggest and most accessible source of av1 video), when comparing size and quality on different codecs (h264/vp9/av1), av1 is either gonna have much smaller size while keeping some level of quality, or have better quality at similar size, or even have both be better.

The first Apple chips with AV1 support only came out in 2023. So the majority of Apple hardware out there doesn't support it. It will be a long time till support is at >95%.