DG -- While I agree that there is nothing to substantiate a specific altitude as high as FL470, there is considerable relevant logic that supports a hypothesis of a rapid climb significantly past, say, FL 410.
I have seen nothing that would rule out a thermally driven rapid climb in the given circumstances, whereas I have certainly seen many posts on this thread suggesting scenarios that are either highly implausible, or even ruled out.
As PJ2 suggests, such a scenario is one possible explanation for one of the as yet unexplained ACARS messages.
FWIW, I am one of those who is still somewhat optimistic with regard to the data recorders being located. Soon I hope.