The problem is that PISA scores won't predict the IQ. If anything, they show that IQ has a large intrinsic component. For example Finns always do well on PISA scores but have average IQ of 94. They point out Lithuania as another example.
There is probably a correlation there because how together your education system is depends on intelligence of people and on economy so they will all get linked together, but you just can't go from PISA score to inherent general intelligence. Though I am sure for south germany (which is not dragged down by east german disaster) and switzerland that high pisa and high IQ will reside in the same place, it just doesn't happen in scandinavia in general and probably a few other places. Places that are organized and have good education but just don't have a lot of extra bright people (and the ones they do have skip out for greener pastures, just like in ireland and spain).
But to me it's somewhat exciting to have that as a good example to show people intelligence has an inherent component, there's other examples but they are too abstract for most people. Most people seem to be bitterly opposed to the idea, but when you know of people who don't study don't work hard and test better than 99.9% of the population and achieve much more then it's pretty obvious.