
In an interview with Premiere Magazine, Michael Madsen stated that he really didn't have an idea what was happening with Sin City 2 and that he hasn't seen a script for it yet: "I haven't seen the script for Sin City 2. I don't know if they are gonna make it. I hope they do. And if and when they do, I will be in it."
He also didn't "[...]know if they ever will [shoot it]. I am not sure [about] the franchise." He also hinted that Grindhouse might affect the making of Sin City 2: "I think the Grindhouse thing didn't kind of work out..."

I really had a hard time believing that Sin City 2 wasn't going to happen because Grindhouse flopped at the box office and wasn't the hit everybody expected it to be. It's only one movie and Rodriguez has made more successful movies (financially speaking) than flops. Sin City was a hit when it came out in 2005. It made 158 million on a budget of 40.
I really hope Sin City 2 does happen because I LOVED the first one, it was my favorite film of 2005 and I am a huge fan of the series. Frank Miller is a genius!