Wow this thread has got lost in outer space.
Lets dial back the wild speculation just a bit, shall we?
In the event that the airport were closed; irrespective of what one might want to imagine is possible; most of the ideas mooted are not, at least at practical cost.
The Islands are subject to erosion and flooding, many here may recall much of the Islands under water 2 summers running, and this resulting in the amusement park being closed, ferry service reduced and extensive sandbagging of Ward's Island. The flooding also effected the airport, though less severely than elsewhere.
The water table, is, needless to say very high here, and the Islands could not easily support mid or high rise development that required deep shoring and foundations w/o great expense and likely raising the elevation level of the entire land area as well.
Doing that, would effect the relationship of that land to remaining area of the Islands, and would impact their erosion rates and water flows.
That's not to say you couldn't build a community of some sort, but the obstacles are substantial and costly.
There is not sufficient servicing capacity on the Islands (sewer, water, electricity) to support intensive development.
There is no High School, the elementary school would have to be enlarged. There is no on-Island public transport, and private cars are currently prohibited.
Traffic volumes for any intensive use, including a major tourist attraction (be they pedestrian, ferry, or other means, are not currently accommodated) ; fixing that would be $$$
There's a slew of other issues.
Anything is possible, but many things are highly improbable. All are way out in front of the facts, for now.