That's exactly right, IMHO. A big part of Iger's, (and any CEO's), legacy is how much they grew the business. When people talking in glowing terms about Steve Jobs, it was about how he grew Apple. Iger was giving a tour of Disneyland by Tony Baxter, and they discussed options for future growth. Such as, expanding Frontierland, Main Street, and the Tomorrowland project, in terms of both capacity and just plain having enough room on the walkways to soak up the growth.
The thing is that WDW will experience growth over the next decade, 1% a year is 10% over a decade. And this is just basal growth, in terms of the growing U.S. and world population, and the segment of those who are interested in going to WDW for a vacation. Who knows, FLE might draw in more guests to MK, when you look at the tallies for 2013/2014, though in terms of total capacity, MK will be stretched even more.
When you look at trying to squeeze Carsland into DHS's parking lot (or across from World Drive), versus building a whole new theme park, you can see why in terms of capacity, a new theme park could help relieve some of the pressure at MK. MK has the highest attendance of all Disney's stateside parks, yet much fewer rides than Disneyland. I think that a park (5th gate) which is physically close to MK would be the best option, especially since you could add trams/boats between the two parks. (I'm talking about the already established expansion pad east of TTC).
Of course, the new park wouldn't be a full-size park just yet. I figure they'd spend $600 million for Carsland, $200 million for some sort of Main Street, plus $600 for a Star Wars land, and they look at adding a Marvel area later. They could even go with a "Villain's park" type main street, have Malificent's castle in addition to a medieval-ish main street that would rival WWHP and be based certain Disney films such as the new Malificent film, Sword in the Stone, Tangled . . . lot's of exciting possiblities. Who knows? They could even put in a Burton-land with a NBC-HMH type ride, in addition to other stuff.