Yeah Delta still is the Official Airline of Disney World, fitting because it is MCO's largest carrier. Delta used to sponser a show in Tomorowland, can't remember the name, but it was a theatre in the round where you flew though america as screens 180 degrees around you displayed the panoramic view. The ride no longer exists.
Your idea is a nice one, but their are a few questions to be brought up. #1, if you tell Leo Mullin about your little idea, he'll claim it already exists, in the form of Delta Express of course. Delta Express is the sort of family, leisure traveller, airline in Orlando that supposedly does little else than bring people back and forth to Disney/Universal etc. Aditionally, they now paint theme planes, sell animal crackers on board, and supposedly employ friendlier F/As. Thats their vacation experience you talk about. Their fares are low and their route network significant, so you would need to do battle with them.
#2. Las Vegas is quite different than Orlando. At the time of National's conception/rebirth etc..Las Vegas was seeing a significant drop in air service. Also, the "hometown airline" AmWest was doing quite poorly customer service wise, maintance wise, and had decided to refocuse more on PHX. Other airlines feeding LAS from their hubs cut service also, because they felt the city was low-yield. This vacuum of service and McCarran's extensive physical expansion sort of begged for a new carrier. Harrah's and Rio Suites bought into Conway's vison a la National. Orlando is not underserved, has not seen a drop in recent drop in service, not served by an airline under siege, and not undergoing expansion for domestic gates. Planes fly full into MCO, but fares are cheap enough adn the schedule is full enough that no one is really crying out for or another option, or in laymans terms.... a "new entrant carrier." They're just doesn't seem to be a need, Delta is doing fine there.
Also, as Michael Ovitz, the southern baptists, and Jose Bove will tell you, Disney isn't the easiset company to get along with. Convincing Michael Eisner and Disney to put their name on your plane will A) Cost more money than Bill Gates made last year B) Not happen.
Good luck anyhow!!!