https://jsonfeed.org/ has had some preliminary traction. Of course, the reason RSS works so well is that everyone uses the same format. So you wouldn't see so much of a "switch" as a bunch of readers accepting either format, for a very, very long time.
That being said, I don't see what's "wrong" with XML in this context.
That being said, I don't see what's "wrong" with XML in this context.