Peel the Orange says the following:
Well, as one of our sources pointed out last week, Marvel was considering replacing the Iron Fist series with a Punisher series. As it turns out, it could actually be a good thing for fans of Iron Fist, as we just received this email from a source who works within Marvel Creative but wanted to remain anonymous:

Marvel will be turning Iron Fist into a Netflix exclusive feature film. This will give Marvel extra time and a larger budget for this project. The Punisher will replace Iron Fist as one of the four Defenders.

Interesting. Take this with a grain of salt but that could be pretty cool. If you remember, this past summer the Netflix CEO said that they were open to making feature films for Marvel characters and this could be a way to start.