Given that a lot of kids are taking advanced math/precalc in 10th or 11th grade, using the tests this way would have a huge bonus of telling the kids if they're ready for college calculus (or at least on the right track) well in advance of enrollment.
The AP Potential tool already tells them their chance of scoring a 3 or higher on the AP Calculus AB or BC exam using PSAT or SAT scores
http://www.collegeboard.com/counselors/app/expectancy.html?calcbc , and AP exams are supposed to be normed to have same difficulty as college classes in the same subject. I doubt that replacing the SAT math with Compass or Accuplacer will improve predictions much.
