True, it wouldn't be as straightforward as HTTP, as there would need to be new semantics (e.g. a handshake protocol for locally-cached IP allowlists or similar)

True, it wouldn't be as straightforward as HTTP, as there would need to be new semantics (e.g. a handshake protocol for locally-cached IP allowlists or similar), but I guess my general point here is that the gp cited a large list of vectors that are all essentially the same problem & could be tackled with a single targetted (very conceivable) solution. Any new such solution would of course come with its own incorrect-implementation dangers - increased attack surface is increased attack surface. The sibling commenter rightfully points out these are still a potential issue with HTTP (servers not checking Host). But spec-wise a solution is still very doable.