Something of a compainion to https://github.com/matrix-org/matrix-js-sdk/pull/4014, but also covering the issues discussed at https://github.com/matrix-org/matrix-js-sdk/issues/3915#issuecomment-1865221366. In short: we should not reject servers which only implement recent versions of the spec. Doing so holds back the ecosystem by requiring all new servers to implement features that nobody actually uses any more.
