In terms of how it would affect Disney, I can't think of anything meaningful.
It's interesting to think how it might affect the tourism industry in Virginia. Do more people want to come to Virginia because of this? Or is it just that Disney takes the tourists that would've gone to the Williamsburg/Bush Gardens area?
Other posters have said it might lead to even more growth in Northern Virginia. I think that's a valid possibility, but let me paint the opposite picture, just as an experiment.
If the holdout sells and it's built on the planned site, it probably means the infrastructure comes soon after. More roads, which of course just means more traffic. The perception is that big roads projects are forwarded just for tourist dollars, not for locals. After the first round of such construction, I can imagine Northern Virginia has a somewhat dimmer view of growth. The plans to turn Tyson's into a new city would be seen in a much more jaded light and probably get shot down. Projects in general might face a tougher approval process. All of those sweetheart deals Virginia gives for the construction of corporate campuses are non-starters.
Preservationists would get in on the action, too, and we'd probably see tougher regulations on building near battlefields in the future, more parkland designated in marginal exurban areas.
Meanwhile, DC's growing all through this time period (as it still is today.) The pressure falls elsewhere. The Maryland 'burbs might take up some slack, but they're quite late to the retrofitting game. MoCo's really only gotten off the ground in the last ten years in terms of city-building, and the bureaucratic hurdles wouldn't be any lessened ITTL. PG's a bit more of a wilderness, and we could see something there, but considering IOTL they're basically following MoCo's lead only 10-15 years behind, it's unlikely.
No, the most likely place for re-channeled growth in the DC metro area is DC itself. The downtown BID is built out a few years earlier. NoMa comes into being a few years earlier. Without the Nats I don't think we see a push for building on the Anacostia yet, but the Waterfront probably gets redeveloped early. A lot more pressure on the Height Act...enough to crack it? I have a feeling it could probably be moderately reformed in the late-90s, before fears of gentrification kick in, and before 9-11. Nothing drastic; 50-100 feet higher, and more places you can build that high. But backlash follows this, and anything older than 50 years is probably rubber-stamped as historical. Getting so much as a window replaced in a rowhouse neighborhood becomes a court case from the historical society.
Some development would still have to occur in NoVa. Only it's more concentrated in Arlington-proper. There's enough pressure on the property taxes that it just becomes impossible to maintain the last of Arlington's suburban neighborhoods, and it morphs from quasi-city into full-fledged city by 2014.
Politically, Virginia's still considered purple, but its razor-thin elections still tend to break Republican more than Democrat.
DC's passed 650,000 residents by 2010. Office space is even more expensive. By this time, MoCo and PG are relieving the pressure more than Virginia. The Hyattsville redevelopment's more successful. Silver Spring's entirely built out. Wheaton and Glenmont redevelopment have been pushed forward 5-10 years. And Rockville's doing what Tyson's is doing IOTL and becoming a new city, with Rockville Pike already turning into the Wilson Blvd of MoCo.
So that's an extremely local perception, sorry to the folks not from the area for all the obscure place names.
