I don't see any benefit to Tarantino "playing it straight" or why anyone would expect him to? Inglourious Basterds was a critical and commercial hit; its historical revisionism was flamboyantly inventive, its genre roots a diverse and engaging tapestry! It was much better than the floaty, rambling Kill Bill; Tarantino's writing works better when he has something from the real world to ground himself in and talk about. Kill Bill was *too* divorced from reality for any real world concerns to much apply; thus much of the dialogue was over-expository and forced-feeling. Or maybe I should say that the over-expository nature of QT's dialogue style stuck out more, in that context. IB worked considerably better IMO.
I am a little disappointed Django is up next though; I had initially read about a profane medieval period piece starring Helen Mirren. I would love to see medieval Tarantino. But Django has promise too.
As to Foxx, I have no experience with him, but he seems kind of cheese-puffy and I have noticed Tarantino's knack for casting becoming more and more questionable as time goes by. He finally wises up enough to leave himself out of the movie, and he starts plugging Eli fucking Roth in there instead. And BJ Novak? Mike Myers? He claims regardless of whether or not he wants to work with someone, he only casts them if they're "right," but I feel like he's prone to pretty arbitrary casting these days.
Do you know which guy from The Wire was in the running? I'm assuming probably Idris Elba, or the guy who played the kingpin? Or the guy who played Omar maybe?