"Florida will most likely take a hit by a major hurricane" is very premature at this time. This system hasn't even formed yet. It is likely it will FORM into a tropical storm within the next couple of days and it will be given the name Hermine (according to the news that's pronounced er-MEEN). After that, NOAA and others will begin attempting to track it. They don't right now have any definite ideas about where it will go or how strong it will be.
As far as travelers to WDW, I've found the biggest thing to worry about is impact on actual travel i.e. being able to get in and out of Orlando by air or even by vehicle if it is eventually anticipated to have that kind of impact. Those arriving by air would need to change their travel arrangements should they be affected, and if they want to do this at no extra charge, they have to wait until their airline posts a travel advisory.
Once the storm is named, it will be easier to see whether it could affect travel days. (my flight to MCO is Saturday afternoon.)
As a WDW traveler I am not considering what happens between getting there and leaving...might need to arrange for a place to stay for an extra day or two but that usually isn't on the scale of trying to rearrange air reservations. If there is a direct hit on the area (which is pretty rare) they'll close the parks and guests will be asked to stay in their resorts. Which is a bummer but it can't be helped.
If it's just rain and wind, but not bad enough to close anything, that keeps a lot of folks out of the parks...and no lines.
