I just don't see how Izuna fits in with the theme of the Naturoverse. That theme being "I've been abandoned/rejected/not accepted, nobody understands/loves/accepts me, but I'll show them!" It began with Naruto in the very first chapter, and has been replayed over and over again with Haku, Gaara, Kimmimaru, Sasuke, Nagato, Kabuto, even the Bijuu. Obito fits in with that theme.
Jiraiya : Orochimaru, Kakashi : Obito, Naruto : Sasuke.Anything sounds better when you try to dress one side up and mock the other one. Izuna Uchiha is a non-character with zero lines of dialogue in the entire series and a reveal of him would turn the entire proceedings into another generic Uchiha brother wankfest, while Obito's bonds of friendship slowly turning into bitter mistrust and hatred reflects the Naruto/Sasuke relationship.