I work in a public aquarium. I don't think that building and maintaining a "dive-only" large exhibit would be fiscally feasible. Perhaps a large, deep swimming pool (no animals) would be possible, but the life support/water quality equipment/staff and and husbandry staff to maintain a large saltwater exhibit is very expensive. Purchasing the animals is also expensive. Half a million dollars is about what you would expect to stock a 270,000 gallon Indo-pacific exhibit. That is a fairly small "big" exhibit.