Let me give you an analogy: If you e.g. figure out some undocumented endpoints for a REST API, which are intended for internal use only, and started using them, do you expect the developers to inform you about changes?

As far as AMD is concerned, this was never supported, nor documented. Now pulling the rug with a firmware update isn't a very nice thing to do, but maybe they've had some actual reason for that beyond "this shouldn't be enabled". Nobody should expect undocumented and unsupported features to just continue to work in perpetuity, simply because they did work at some point in the past.