Hey, we posted at the same time!
My problem is he doesn't go into his argument. Yes, he tries to say that fans won't read radically different takes, or that new readers won't like becoming fans of one version of the character and finding the real character isn't like that, but my problem with his stance is he never goes into detail about what makes YA vs Adult books "radically different". Outside what is an acceptable level of violence, or some minor points of focus, and of course the ever nebulous debate of continuity, there have been plenty of these books that don't seem all that radically different. Of the books I've personally read, Superman Smashes the Klan, Batman Overdrive, Batman Nightwalker, Under the Moon A Catwoman Tale all fit comfortably in the normal albeit slightly Elseworld-y parameters of what I'd expect from these heroes. The only one that doesn't fit the more superhero/antihero mold was the Lois Lane book, but then she's not a traditional "superhero" to begin with. If his argument is that changing these characters won't work, he has to back it up with examples of what has been changed and how it doesn't work.