I think the floating pool thing really depends on where you live, the climate in the winter and the water table in your area.
That's a whole lot of concrete to be floating out of the ground...and I've never heard of a skate park floating up...so I find that story a little hard to believe. I've heard it before too...
Princess nixed it? Who wears the pants in your household? You or the princess. Tell her you're gonna cover it with a deck and that's all there is to it!!!
Yeah, right...
I'm usually in the "yes, dear" camp too.
If it were me filling it, I'd consider what Tom just said -- be careful when filling it, it would be nice to have it be usuable in the future if you consider selling the place.