The Churaumi Aquarium in Okinawa, Japan, has a fish tank so big that it's called the Kuroshio Sea. The gigantic tank is 10 m (33 ft) deep, 35 m (115 ft) wide and 27 m (89 ft) long and holds the equivalent of 3 Olympic-sized swimming pools worth of water.
The tank is so large that not one, but four whale sharks live in it. The Daily Mail has more gorgeous photos of the aquarium exhibit: Link
I disagree about your "newer research" showing the need for migratory patterns - they do migrate over large expanses, and dive down to amazing depths, but that appears to be in search of food, not a biological requirement or for entertainment. The Georgia Aquarium is working with the Mote Laboratory and a facility in Mexico on scientific field research on whale sharks so we can understand them more effectively - there are still a great deal of mysteries about them.
But I agree, the facility is the size of a football field, and even diving in it a large amount of time can go by without seeing a whale shark. They are not cramped in a small enclosure.
I could see the discussion of how many whale sharks to stick in the tank going like so "Two!!! No we need to double that or no one is going to come and see this!"
I wonder if they would in a facility of this size.
(Well, you can put a bunch of *other* sea life in with a whale shark... and they won't get EATEN!)