But isn't client-side adaptive bitrate switching the point of HLS and DASH? Given that server side software (encoders, live and VOD origins) and clients (shaka, hls.js, dash reference client, set top boxes, smart TVs) exist ... doesn't it make more sense to set up http/3 and have it all in a well established standard?
Re-transmission of old frames is the opposite what you want for live streaming. If you can't re-generate the frame from forward error correction, then you're shit out of luck. if you're hitting network throughput limits, wasting data on transmitting frames you cant display is not a good use of a limited resource.
As for maintaining existing standards, it depends on your goals. If you're not trying to push boundaries then absolutely, HLS/DASH is great for quickly getting off the ground. But if you're looking for something in-between HLS and WebRTC then MoQ is compelling.
Apple has committed to adding it, and there's already been some work on it in WebKit, but we don't know when it will make its way into a Safari release yet.