It occurs to me that QUIC could benefit from a single kernel-level coordinator that can be plugged for cooperation - for instance, a dynamic bandwidth-throttlin

It occurs to me that QUIC could benefit from a single kernel-level coordinator that can be plugged for cooperation - for instance, a dynamic bandwidth-throttling implementation a la https://tripmode.ch/ https://tripmode.ch/ for slower connections where the coordinator can look at pre-encryption QUIC headers, not just the underlying (encrypted) UDP packets. So perhaps I was hasty to say that you just need SOCK_DGRAM after all!