One thing I don’t really understand: if conference organizers accept (or invite or whatever) a keynote speaker, and the acceptance/invitation doesn’t reference any particular topic, then presumably they are actually saying they will give a keynote slot to the speaker to speak about whatever they like. And if the speaker gives a talk about something they’ve worked on but that doesn’t have any sort of consensus to become part of Rust, so what? It’s a keynote talk, not a merge request.
If the organizers wanted a talk about an actual accepted feature, surely the invitation should have said so.