Reading about QUIC (the basis of HTTP3) a little more, it looks like it is attempting to replace TCP entirely. It does this by making the reasonable assumption that all connections should be secure (via TLS), and so it merges layer 7 TLS protocol down and integrates it at the transport layer. It also has its own flow-control and reliability mechanisms, like TCP. If QUIC "wins", I don't see an obvious use for TCP.
TCP remains for cases where speed is required so TLS is skipped.
Instead of application layers, I'd assume evolution on transport layers, so next to plaintext TCP there would be less reliable faster transport protocol, secure but slower transport protocol and possibly others.
Similarly, is UDP a zero cost layer? If not, one could perhaps get more speed from working directly with IP.
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[ 4.7 ms ] story [ 17.1 ms ] threadInstead of application layers, I'd assume evolution on transport layers, so next to plaintext TCP there would be less reliable faster transport protocol, secure but slower transport protocol and possibly others.
Similarly, is UDP a zero cost layer? If not, one could perhaps get more speed from working directly with IP.