I'm no engineer, but when I looked at it, my thought was that what you want is some sort of hinge system, with a pulley and crank, that would let you raise the stairs up to the basement ceiling when it's time to play pool. You probably wouldn't need to put the hinge on the entire stair case, just high enough up so that you have about 5' of vertical space clear.
You wouldn't be able to have any supporting walls on the sides, but you could probably put together some sort of folding railing. This would be sort of an oversized version of the attic stairs idea.
One advantage of this would be that you would never have a big hole in the floor that someone could fall through.
Anyway, I'd like to see some pictures of whatever you come up with.
Cory
