What does "last minute" mean here? Isn't RustConf in mid-September and it's a single track conference so speakers are heard by all participants? It would be a good way to get your work and opinions out to the broader community.

Clearly the process was botched and more effort should've been made to come to a mutually beneficial solution, but going from an invited keynote (great honor) to an invited talk (honor) is not what I would call a deliberate attempt to "disgrace one of the experts in my field."