I agree, it's nonsense. For what purpose - I don't know, probably none and if there has to be one, maybe disinformation and distraction. So I'm sorry for spreading it. I read this article and it initially made me wonder, so I posted to see what others thought. Probably the fact he didn't look much older, perhaps even younger than his picture 20 years earlier and the bottom teeth on the photos, they look all worn down then suddenly they stick out like a rabbit. It was admittedly odd and Mathis sounded like he was being reasonable. I didn't at the time look any further.
Anyway, afterwards I asked a friend who is a physics buff whether any of Mathis's scientific work is any good. 2 minutes of reading Mathis he notices all his claims that accepted scientific tenets are false, but Mathis hardly details how or why they are false, but goes on about that his methods and calculations are right (apparently). It all made little sense to my friend.
Back on this Hawking claim, seems to me that Mathis cherry picked photos to retrofit his foregone conclusion about Hawking. The reason being is there are literally thousands of photos of Hawking on a Google image search, and many show a progression of age, not the sudden change that Mathis cherry picked photos to make his foregone conclusion that Hawking was replaced appear valid. That's a very non-scientific approach and if he uses the same approach with his science (which seems to be the case), his science would be very non-scientific too.