Joe Carnahan's DD pitch to Fox! Goddamn, Marvel's got to sign Joe to do their DD!
I personally like it a lot and would go see this in a heartbeat. Having said that, I can understand why Fox didn't go for it, loath as I am to defend them.
Even leaving aside the fact that the previous DD film wasn't a huge earner, a 70s-set superhero movie is likely to be a risky move at the box office. X-Men First Class had a lovely, groovy James Bond-esque look and feel but made less money than the blander Origins: Wolverine or Last Stand. A hard-edged gritty almost blaxploitation-feeling movie could be an even harder sell, particularly with teenagers.
Let's face it, you just know that even had Fox greenlit this, they would have interfered and interfered until the final product looked nothing like Carnaghan's final product!
Marvel may well hear Carnaghan's pitch, now they have rights to DD back, but I also find it hard to see them agreeing to a 70s-set movie, thus keeping him out of the action alongside the rest of the MCU (unless they decide to have an older Matt Murdock in a sedentary role in modern days).
Still, if Marvel were feeling brave, they could think about maybe a series of low-budget movies or HBO type show, set in the 1970s and featuring DD, Iron Fist, The Falcon and The Punisher (with no need to update the Vietnam origins of Mr Castle).