I was once invited to give a talk (which was more or less a keynote, although I don’t think the word “keynote” was used) at a major conference. I was specifically invited to talk about my work on X. IMO it would have been really odd for anyone on the program committee to subsequently say “well, I’m skeptical that project X will pan out — maybe the talk should just be a regular track talk about X or a plenary talk about Y instead” after the invitation was given.

It’s not as though giving a talk implies any particularly strong endorsement by the community at large that the subject is going to pan out. And if the talk is just about “whatever the speaker is working on”, then there is absolutely no implied endorsement of what they end up talking about.