I also heard that. We just took a Keys to the Kingdom tour at the Magic Kingdom, and the question came up about a 5th park. Our tour guide said Iger wants to enhance the parks here, rather than think about a 5th park.
As for people complaining about long lines at MK, consider going at an off peak time. We usually go in October and November and the weather is beautifull and the lines are short. Disney does not benefit from long lines. That, I am guessing, is why they came up with the Fast Pass system. They want happy guests, and guests who have to wait in a 2 hour line I would not think would be too happy. (It is the happiest place on earth, right?) We were just their this week and rode just about everything and never waited more than 20 minutes for anything. Read the Passporter and Unofficial Gudes recommendations, they work. The Magic Kingdom is the most visited tourist attraction in the entire world, I am sure it is no easy task to keep lines short, but if you ask me, they do a pretty good job. That is probably one of the reasons for the incredable amount of detail they put into the que lines, like Splash Mountain, TMR, etc. Most attractions have things to occupy your attention while you wait, whether it is with a pre show or the details.