Indeed. But (not sure if that's what GP meant just guessing) it's sad that tons of middleboxes that peeked too much inside packets effectively broke "end-to-en

Indeed. But (not sure if that's what GP meant just guessing) it's sad that tons of middleboxes that peeked too much inside packets effectively broke "end-to-end" goals, so now it's impractical to deploy any new protocols (such as SCTP) alongside existing UDP and TCP. Most practical progress is made by layering more and more on top of existing protocols :-( Actually I'm kinda relieved QUIC succeeded at all with much less layering on top existing stuff than usual. (Compared to say Websockets-over-HTTPS-over-TLS-over-TCP-over-someIPv6-over-IPV4-tunnel...). If it's feasible to deploy a major new protocol over just UDP, that's practically as good as directly over IP! P.S. I think encryption is the main force that held back the (economically almost inevitable) desire of middleboxes to "add value" by manipulating inner layers.