Agreed. 1, 2 and 4 seem uncontroversial to non-TCP experts like me. But I do think we'd need a lot more re-assurance from old-hand TCP crafters as to whether 3

Agreed. 1, 2 and 4 seem uncontroversial to non-TCP experts like me. But I do think we'd need a lot more re-assurance from old-hand TCP crafters as to whether 3 (TCP Fast Open) makes much sense, let alone worth the huge deployment effort. Changing the fundament of the Internet purely for the sake of a higher level protocol (albeit an important one) in the stack seems dangerous. This would be the case, if for no other reason that it sets a precedent for future changes. Changes at each layer should always be as stack-agnostic as possible. This is by design.