Forget all of that because now, from Scott himself, comes the announcement that Crowe will be playing both roles. Mum on the details, the director would only say it was "a good old clever adjustment of characters. One becomes the other. It changes." I would take that to mean that the Sheriff of Nottingham becomes Robin Hood after having to steal from the poor one too many times ... or they're twins, which would be pretty lame, especially for Scott and Crowe.
But wait -- there's more! CHUD points out that in reading the original screenplay, they noticed the Sheriff was caught between a tyrant king and a less-than-heroic Robin Hood. Nothing in this script indicated the Sheriff and Robin Hood could be played by the same actor. Now, Brian Helgeland came in and did a rewrite, and much depends on that.
The medievalist in me suspects this is less shockingly revisionist than a return to the old medieval legends, where Robin Hood was merely an outlaw who beheaded people from time to time, not the Robin of Locksley we all know and love. It's a pretty flexible legend, and I'm very anxious to see what Scott does with it ... when it finally heads into production, that is.