Personally I am not too worried simply because I do not think we will ever see a 5th gate. As it sits right now there is more than enough to keep a family quite busy for 7 days and still have things left to do on their next trip. I feel a 5th gate would do nothing more than spread the same butter a bit thinner.Stuff like this scares me, and angers me. Walt and Roy bought all that land so that "there would be enough land to do anything they ever wanted." One might argue that since Walt really wanted to build a city of his own, these residential and commercial developments are in line with his plans - but I don't think his ACTUAL plan was to sell off the property to 3rd parties.
If you were to just glance at an aerial photograph of property, you'd think "Heck, they have PLENTY of land left." But that's not entirely true. While there are large portions of land scattered around property (some large enough to accommodate entire theme parks), they still can't develop everything you see.
Water management is a major issue for WDW, since they're sitting on a swamp with an obscenely high ground water table. For every square foot of concrete, asphalt or building they construct, they have to find somewhere to displace that water. Right now they're doing it all with canals and retention ponds, but you can only dump so much water into those waterways. Eventually you reach a point where you can't cover one more inch of your own land (since you can't displace water onto someone else's private property).
Since there aren't any new theme parks on the board, there's probably "plenty of land" but if they build one more park, that would pretty much max out the big chunks of land.
Selling off these large parcels for non-Disney stuff like 4-Seasons and Flamingo Whatever really makes me cringe....and I hope it doesn't come back to bite them in the a$$ someday.
The way I always understood Walt's want for so much land was two fold. Not only to be able to build all he wanted but also to keep the parks secluded from reality. Right now WDW is about as big as it could be theme park wise. It could support a few more resorts and possibly another water park or a boutique park but from a theme park standpoint I think WDW is about maxed out. The seclusion aspect is still in full force and IMHO is in no danger of being compromised.
The 4 seasons is going up on a piece of land that would have never been used for anything other than a resort and we will be getting one heck of a resort out of the deal. Arguably it will be more luxurious than any resort on property and will attract some big spenders to WDW.