I really don't care that much about who's in the movie version of Wicked. I think it would have been nice if they'd made it many years ago when Idina Menzel and Kristin Chenoweth were more "age appropriate" to the lead roles and could have played them. And I will note that the most popular stage-to-film transfer of all time might be the movie of Grease where no one who played a high school student looked like one.
But really, a lot of this reminds me of the story of the novelist who sold his book to Hollywood, they made a terrible movie out of it and people said to him, "They ruined your book!" To which he replied, "My book is right there on that shelf, exactly the way I wrote it." Musicals that are great on stage easily survive substandard film adaptations. You can name examples as easily as I can.
I am though irked that someone has started a petition to keep James Corden out of the movie of Wicked.
The petition really doesn't say why, apparently because the initiator of the petition thought it was self-evident. Not to me, it isn't. I think Corden's a very talented, funny man. I gather those signing the petition didn't like the movies made of Into the Woods, Cats and The Prom, all of which he was in. I kinda liked all three of them…and what I thought was wrong with them had nothing to do with Corden, except maybe that he wasn't ideally cast in The Prom.
I assume they don't have him in mind for Glinda or Elphaba but there are several roles in Wicked I think he'd be fine for. And as far as we know, the filmmakers may not have him in mind at all. I just think they should.