This MSC aims to make HTTP Range capability mandatory on the content repository fetch endpoint.
HTTP Range is a Header-based method by which browsers and other clients can request a certain byte-range of a file.
Most modern browsers depend on this mechanism to scrub through video footage, and the absence would make some media playback unable to be scrubbed through.
This would only affect CS endpoint /_matrix/media/v3/download/{serverName}/{mediaId}
.
Related: https://github.com/vector-im/element-web/issues/4265
This MSC is to make the behavior standard, and consistent across the matrix ecosystem.
This MSC would only add a well-known HTTP capability to an existing endpoint, which can easily be ignored by existing clients, I think it's overkill to require an unstable prefix for this.