Firstly, Wicked will be released before 2016.
My casting ideas -
Elphaba - Lea Michele (more of me really just wanting to hear her sing it rather than a smart casting choice)
Glinda - Amy Adams
Morrible - Madonna - hell she is the queen of spin - perfectly cast
Nessarose - Anne Hathaway - perfect in this role - beautiful and not a hard singing role - in fact the song may even be cut from the film.
I do not think that too many names will be needed for the film to guarantee financial success. The biggest name is 'Wicked'.
But I agree, the mere thought of Menzel or Chenowirth in the film is scary and disturbing and just plain ewwwwwww.
'Downtown Elaiggghhhy?'