I love a good "Hey look at Shakespeare *this* way" theory, and the TV Tropes brought me some new ones to play with. Hat tip to Michigan Shakespeare Festival for posting about this on their Facebook page!
How about the idea that Iago doesn't exist? That he is just the personification of the individual evil side of each character?
He's the incarnation of that voice within every person's mind, which is why it's so easy for him to trick everyone into believing what he says. He's not saying it — they're thinking it. Emilia is just a klepto with self-esteem issues; Othello is suffering from paranoia (or, if you hold that his seizures are real, he's also having epileptic hallucinations); Roderigo is generally unstable; Cassio has a serious drinking problem... the list goes on.Now, obviously we're out of the realm of what Shakespeare may have actually intended - there's no way he had the narrative to even think of something like this. But in terms of modern interpretation, could you pull this off? I wonder whether some sort of weird version could be made where there is no Iago character, but instead each of the characters listed above takes turns reciting Iago's appropriate lines as if schizophrenic.
How many scenes does Iago have by himself?
There's a few more good theories on that page (like Horatio being a hired assassin sent by Fortinbras) that maybe we'll get to another time.