I just hit on this post. Wow, the possibilities!
I could get one of the giant catfish that sit below one of the dams on the Tennessee River, the ones that are supposedly big enough to eat a person. (Don't know if that's true or not, but I diver once told me the cats are huge down there, they just lay there all day with the water flowing over them and eat a lot).
It could be a "pleco shelter" for all the overgrown plecs who don't have big enough homes anymore.
A huge school of tinfoil barbs? They would shimmer like crazy in something that big with some good lighting. Maybe a few oscars to keep it interesting in there.
Or a dolphin "playpen"? Sea turtle haven?
Logistics? How to heat it? How to light it? How to CLEAN it! Ack. How much ammonia to fishless cycle it? And who is going to pay for all that fish food???!!!
P.