I'm not sure that the existence of a core spec negates this though - you could similarly write an MSC for whatever thing you wanted, like a new low-bandwidth tr

I'm not sure that the existence of a core spec negates this though - you could similarly write an MSC for whatever thing you wanted, like a new low-bandwidth transport using CoAP and CBOR (MSC3079 - https://github.com/matrix-org/matrix-doc/pull/3079 https://github.com/matrix-org/matrix-doc/pull/3079) and it may or may not end up being accepted into the core spec, but the MSC exists regardless and people can implement it. (and indeed, people often implement MSCs that they like before they land in the core spec, and before something lands you generally want an implementation or two anyway)