Things Disney would have to do to put a resort on
Castaway Cay (remember, no infrastructure to build upon)
Greatly expand saltwater to fresh water capabilities
Greatly expand sewage treatment
Food storage because everything would need to be imported
Do something with the nightime bug problem
These can be overcome with time, technology and money. What wouldn't/couldn't be "fixed" is the wear and tear on Castaway Cay.
The following applies to a resort or the ships making 2 stops per trip there. The islanders do a great job of maintaining the beach and the facilities for us. With limited use three days a week, the crew and mother nature can work to restore the "damage" we inflict upon the island/beach every time we stop there. If there was a resort on the island, people would be on the beach 14-18 and in the water hours per day verses the 7 hours three times a week.
I Love Castaway Cay. Want it to stay "fresh and clean" so it remains a great beach day whenever I cruise Disney. And I am looking forward to the time when the snorkel trail is really teeming with sea life. That won't happen if we are out there everyday disturbing it.