Looks like a Will Law (of DASH fame) pet project. Interesting to see where it will lead. Seems to have sponsorship from some industry heavyweights Meta, Cisco, Twitch, Google, Akamai, Ericson. But notable absentee is of course: Apple (!)
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.