I think its doable on the client with the latest iphones with an ABR ladder of 2 rungs (540p/720p). latest iphones have good hardware HEVC encoders apparently.
Discussion
I should look at android hardware and see what is available there as well..
probably way more variable support. also HEVC is not supported by many clients and is worse in terms of patent-trolling
AV1 is great but the hardware encoders bascially only newly existing and the decoders as well, so it's either a battery sink or no compat
so I guess I'm stuck with h264 hls for now