I have also thought they should only installs pools up north here with insulating foam as an intermediate layer between the earth and the pool, sure would reduce the heat lost to ground during these colder months.
For a conventional pool I would use them to back the side panels, some cutting to go around the braces would be required but not hard to do with foam, the bottom can be straight foam or a liner fabric could be used over top. Not sure on their crush resistance for a bottom though, that might be a sticking point...might have to check their applicability to this usage type. I'm thinking that spray foam would be a lot easier to apply though. If your thinking about a free form gunite style pool you still need to put steel down for the cement to frame the cage, I wonder about ground heave with frost though...hence why you don't see many gunite/concrete pools up north.
I do know that most of the heat loss is through the water surface as radiation and evaporation, you might want to look into what percentage really goes into the earth side and bottom as heat loss...I have a feelings its a fraction of the heat loss from the waters surface to atmosphere. I'm thinking that you would be better off to use a standard pool configuration with spray foam on the sides (forget the bottom) and come up with an automatic cover that is insulated, I'm getting tired of my cheapo "bubble wrap" style solar cover already and wish I had a motorized insulated cover to keep the pool clean and warm.
I am seriously thinking about this kind of system for my pool, insulated slats baby...thats where its at!