I believe having multiple nationals can be one possible solution.
You all remember how last year there are 4 divisions, and each team only compete with other teams in their own division. Well, I am suggesting that FIRST have 4 different competitions at the same time after all the regionals ended.
The teams will be randomly split into the 4 divisions just like last time, and the location of the 4 divisions will be 4 separate places across the country. This way, teams will have to travel across the country for one of the randomly assigned divisional competitions, and teams base in Florida will actually have to get out of Florida some time to compete somewhere else.
Well, one of the division can still be at Florida.
And, after the 4 divisional champions are decided, they will get together to compete at Epcot's Einstein stage for the National champion. And all the teams will go to the finals and award ceremony for about 2 or 3 days, and won't have to pay as much for expensive Disney hotels and food.
However, I am not exactly sure how this will work out, as some teams might not want to go to Florida just for the finals and award ceremony. And, it will also mean teams will have to travel one more time instead of just going to a regional and national.