No, NBA players will not start shooting free throws by using the granny-style underhanded method. Even though physics has been used to demonstrate that underhanded throws are more accurate, professional basketball players are unlikely to adopt that method as they would look odd while they were playing basketball. Part of professional sports is about portraying an image, and granny throws would not support the type of images most professional athletes want to project.
Could you imagine watching an NBA game and seeing the players take shots that way? How entertaining would that be? However, for the players, they have learned how to master their shot over years and years of practice, and I couldn't imagine that shooting it any other way would be beneficial to them.
Many players that are in the NBA are prided upon their style, personal form, and the way that they play and though granny style may be more effective, they are going to shoot however they can to make themselves look best. This is a simple fact that cannot be argued.
No, NBA players will not shoot basketball free throws "granny-style" because it lacks style and finesse, and it looks amateurish. Most NBA players work hard to develop identifiable styles during their careers to attract the attention of fans and endorsers. Resorting to "granny-style" free throws will do nothing for their image, even though it might improve their point averages. A player would be condemned mercilessly by media and fans alike should he adopt this sort of free throw style.